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In the manual, it states:
RESET LENS
When set to [ON], this resets the focus of the lens (infinity) each time the power is turned off.
What does this mean?
Does this mean that if I were to turn off AF once the camera is turned on, that I should be able to fire off a quick shot and have most of it in focus (smaller aperture, would give me more DOF though)?
The description is quite accurate. It simply means that the camera will focus the lens at infinity each time it is powered on. Many modern lenses can focus beyond infinity and have no stops at infinity, so when shooting very distant subjects such as stars it is difficult to focus, particularly since light is very low.
While I almost always turn off that feature, it could be useful because depth-of-field is relatively deep at infinity. So while you may not be have to get the maximum focus-depth as you suggest, you can easily frame your shot. Should the lens have been close to its near limit, the preview is highly lke to be quite blurry.
Keep in mind that if you have severed the electronic link to the focusing element, this feature does nothing, For examole the M.Zuiko 12mm F/2 allows the focus-ring to slide back toward the mount. In that position, the camera cannot change the focus distance at all.
To get "most of it in focus" you need to use the hyperfocal distance, not infinity focus. When the lens is focused at infinity you give up any depth of field past the point of focus and push the near limit of DoF further back than it will be at the hyperfocal distance.
I think the point of resetting the camera to infinity focus each time it is turned on is that correct focus for most of the distance between the camera and infinity is a much closer movement of the focus elements from the infinity position than from the minimum focus distance position. The movement of most focus rings is a logarithmic, rather than linear, one. My 50mm f/1.4 lens, for example, has a minimum focus distance of 1.5 feet (0.45 meters). Turning the zoom ring halfway between that MFD and infinity sets the focus at about 2.5-3 feet (approx 0.8 meters). Any focus distance past 10 feet (3 meters) is only about 1/6 of the total movement of the focus ring from infinity. As you can see, the vast majority of distances are focused properly at a position very near to the infinity focus position. This makes infinity a good starting position for the focus elements.
