In one event I was covering, some of my fellow photogs were shooting in burst mode. They take around three images per press of the shutter just to capture a man standing still on the stage (maybe they want to capture the flies flying around??). This is understandable for sports or subjects that move a lot, but in this case we were shooting subjects who are mainly standing still. What is the purpose of this?
It could be to reduce camera shake. I use this technique in a lot and in poor light it can be very effective. Pushing the shutter button causes the camera move a little, so by holding it down for a burst of three, the first image may have some residual movement from your finger, whilst the last image might have some shake as you start to release the shutter, but the middle image is usually ok.
Additionally, as camera shake is a random motion simply by shooting more images you are more likely to have a sharp image.
Other explanations might be to do with unanticipated motion, capturing the best facial expression. Another way of looking at this question is by asking what are the disadvantages of shooting in burst mode?. Other than battery/memory card usage there aren't many. Shutters still have a limited life but that's extending into the hundreds of thousands of actuations these days. Compared to shooting film with the cost of developing and frequency of changing rolls, taking a photo with digital is about as close to free as it gets.
Was the man really standing still? Sometimes they talk. It's annoying when they talk and they also blink and look weird with their mouth half open.
Bursting it may avoid cases of disfigured man half talking.
Maybe he was bracketing something?
Maybe the man is still now, but tends to move randomly? and so he left it on burst mode.
I don't know why people shoot in burst mode but I shoot in burst mode for the following reasons:
It lets you capture the moment and the moments before and the moments after. Sometimes you may go wrong with your judgement about the best moments. I know this is a bad practice but there are a lots of things happening in an event that I have to concentrate on rather than wait for just the perfect moment. Burst mode on - shoot - delete the unwanted.
Candid shots. You cannot just bank on a single moment for candid photographs. There could be a series of expressions from your subject in a short while that you ought to capture. If I'm shooting single frame mode and if my subject changes expressions after a click then I ought to press the shutter again and meanwhile the expressions can change again. Keep it in burst and shoot all the moments.
Action. Whether it's a war, a football game or even kids playing, you never know what's the next action. When you want to be able to capture a series of successive moments you need a burst mode.
Flipbook effect. Burst shots give a nice images to create a flipbook or create animation using this effect.
First, if he took a single photo, it could have been blurred if the camera shook and taking several photos will mean you definitely have one that is clear and not blurred.
Also, when he analyses the photos later, he might find that in one, the man blinked, in another, he looked away and in another, someone's hand was in the way.
Burst also reduces camera shake as pressing the shutter key can shake the camera minutely.
Finally, imagine the annoyance when you find out that you didn't quite take enough photos to make sure you had the perfect shot. It's best to take too many photos than not enough!
If it was exactly 3 photos per shutter press, they were most likely using bracketing rather than simple burst shooting. Bracketing can be used for a number of different purposes, but the concept is that it takes some aspect of the camera and changes the setting between shots. Exposure, Flash Power, White Balance, Focus, etc can all be varied slightly to give a range of shots. HDR photos also are typically generated using an exposure bracket.
Simple use of continuous burst shooting can also be useful for making sure you get a good image. Since you can't control things like when the speaker blinks, one shot might end up catching him blinking, so taking multiple shots gives a better chance of getting a good shot.
I personally don't use bracketing very much, but my camera is ALWAYS in high speed continuous mode. I may only take a single photo at a time, but having the ability to take more quickly is valuable to have. This is particularly true when shooting high speed activities where getting the exact perfect moment is challenging. It is also key when dealing with one time events where getting 1 or more OK shots and quickly following it up with an attempt at a perfect shot is key. Without a high speed continuous setting, you are stuck risking missing the perfect shot while waiting for a better shot to happen (that might not.) With practice, you can control exactly when and how many photos you take while using a good high speed shooting mode. (Plus it's kind of entertaining to hand your camera to someone and have them accidentally take 2 to 4 photos and wonder what the heck just happened.)
I would imagine to give them the choice later to select the best shot. If it was someone standing on stage (at a gig perhaps?) then likelihood that they can move, the lighting is low, you want to have the best chance of not having a blurry image - so take several. You never know how things that you don't notice at the time of taking the photo can affect it. Perhaps he has blinked his eyes just at the moment you trigger the shutter, so you can't use that shot....if you had rattled off several at the same time at least one of those would be usable. All sorts of reasons really. It's the wonderful thing about digital - no development costs (other than time).
Better to take too many and select the best shot you have and bin the rest, than not take enough and be disappointed that you didn't get the shot you wanted...
I've taken to burst-mode shooting in low light even if the subject moves only slightly. This has been very effective for me during evening HS football games when I want to get a picture of (for example) a coach in a protracted or intense discussion with a ref or other player. While I know the scenario should make for a good, possibly great picture, it will only last for a few seconds, so I want to mitigate the risk as much as I can of a camera shake, or an inadvertent blink/closed eye, things of that nature.
I often take multiple images to ensure:
1) good facial expression. Catching someone between a smile, or with an expression that doesn't match the content or the presentation can be a problem. Multiple shots ensure better expressions
2) catching the eyes open. Nothing worse that a family photo with half the subjects eyes closed. Multiple shots helps ensure getting more of them open.
3) ensure options for editing. If you have a subject wearing glasses, and a bad glare appears, or if you have multiple subjects where one is looking away or eyes closed, you can simply graft the open eyes or head from an image a fraction of a second ago onto the better image to create a composite that shows the best possible subject views.