I use subtitles for video games for a few reasons: until recently we've had a crappy old TV and because of it, half the sound was missing so you had to move the camera around during dialogues to hear both sides (applies only for console).
Also, you never know when a neighbour/someone on the street is going to be noisy, which tend to happen during critical times.
Then there is the fact that some voice actors just cannot pronounce their lines properly, making whatever they say undecipherable.
And there's the fact that sometimes you get either some hidden dialogue that's not being said, or you get the complete sentence of a guy who gets killed mid-sentence.
Lastly, English isn't my native language, so I want to see what's being said in case I can't understand when a particular word is said (doesn't happen as often as it used to, but still).