I can't locate it anymore - probably still out there - there was a video clip of Michael Jackson recording track after track of him singing the exact same vocal line, with Quincy Jones running the recording session.
In the video clip, Michael Jackson first of all, NAILS each take with spot-on pitch and intonation, and secondly he would physically move his body between 6" and 1' for each take, so that every one of them was slightly different, both in proximity to the microphone, and also because of slight differences in vibration and tone and such.
Layering those all up - with slightly different panning, and volumes, gives an INCREDIBLY rich vocal part.
The clip is for the We Are the World song, by the way.
I don't think I will ever forget how well that approach worked for vocals.
Bob Bone