I think he's asking about recording in stereo....as in using a stereo miking technique...not about doubling a single vocal track.
If he is asking about doubling a single tracks...mmm...that's not really stereo recording anyway.
The answer is no...there's no real need to record vocals in stereo. That's not to say you shouldn't/couldn't do it. There may be a situation where the vocal and the space you are recording can provide a stereo recording quality that will enhance the mix/song...but generally, it's one mic, one track.