What exactly does the stereo expansion effect do? How much should it be used in general?

I'm recording a band and I would like to add a little more "fatteness" for the vocals in order to give a more stereo spaced impression. I tried to put the vocals on 2 tracks, pan towards Left and Right each and then I tried some delay from 1 to 30 ms between the two tracks. The result was like adding a chorus effect.