If your subject is at the minimum focusing distance from the camera (say about 450mm) at f/1.4 your depth of field is an insane 4mm, very creative in some cases, but not for portraits. By the time the subject is say 1.5metres from the camera the DoF has grown to a slightly more usable 50mm. So for close head and shoulder portraits with the 50mm f/1.4 lens you can't really go below about f/2.5 . Once you are a decent 2.5metres from the subject(s) your DoF is a very usable 140mm. Of course you will almost never want to open the lens fully to f/1.4, but you get the picture (no punn intended)
I'm not saying that the lens is not great for low light in wedding situations, only that you need to consider the DoF very carefully when framing your shots and positioning yourself from the subject(s). As said though, you will really struggle to shoot an entire event with just this lens.