I'm a portrait photographer and recently I got 2 weddings to shoot, so I'm ready to purchase another lens wider than the ones I have. I'm thinking of buying a Canon 24mm f1.4LII. Do you think this lens will be really good for wedding photography? What shots would it be useful for?
No, you don't want such a wide lens for a wedding, at least not for much. I shoot weddings using my 24-70 f/2.8 and my 70-200 f/2.8. During the ceremony, my 70-200 gets the most use with the 24-70 being used for a few shots to capture the entire room. You are constantly shooting from a distance both for the perspective it gives and also because you don't want to be in the way at a wedding. (Unlike in a studio session, you aren't there to get the absolute best pictures possible, but rather to capture a major life event without interfering with it, forgetting the second part is BAD!!!)
While my 24-70 is my group portrait lens of choice, I'm very rarely at the 24mm end of things and I almost never put my 17-40 f/4 on the camera anymore. That may change if you are on an APS-c body as 24mm would be like my 36mm which is a bit closer to what I do some large group portraits at, though it's probably often closer to 50mm.
The bigger issue is that it is a prime. Primes and weddings don't go together very well. Things happen fast and things happen once. You have to catch them when they happen and if you are in the wrong spot or have the wrong lens on, you can miss important shots. Primes can be useful for the portraits portion, but your life is far, far easier with fast zooms as your primary lenses for weddings (even if that means renting them for a few weddings.)
A polyvalent zoom(50~200mm), something with a pretty high zoom if you want to take some portraits because like dpollitt said :
an extremely wide angle lens for portraits, sure you can use it some for a wedding, but you would be silly to use it for most of the day - as you'll get tons of distortion.
But why a polyvalent zoom because at a low zoom (~50mm) you can more easily take group pictures.
P.S : Sorry for my english, it's not my first language.
It depends on your style of shooting weddings. If you tend to take a lot of candids or use a photojournalism style, I think a 24mm would be useful.
However, I wouldn't advise buying the Canon 24/1.4 straight off. Used Canon 24/2.8 are pretty cheap, and Sigma 24/1.8 won't hurt your pocketbook too hard. If you're in love with Canon's 24/1.4, try renting one before laying down all that cash.