A very common approach is to record guitar and vocals together to create a 'Ghost Track'.
There are often small mistakes in the playing when you are doing both at the same time.
These are fine when you are playing live, gone and forgotten in a fraction of a second, but become a permanent irritation when recorded.
You then use that ghost track to overdub a perfect guitar track, which will be then clean and isolated on its own track.
Then you turn the ghost track off, and record your vocals over the perfect guitar track. Now the Vocals are clean and isolated on their own track.
Again, you can concentrate on performance and phrasing when you are not having to remember how the little guitar runs go.
Sometimes, if you are really lucky, the ghost track is good enough to fade up a fraction in the mix to reinforce the final version.
I don't see the point of using a stereo recording set up to record a vocal track. The purpose of recording with a stereo pair or a Mid/Side set up is to give the impression of width in the stereo image.
A piano is wide, a drum kit is wide, but even Pavarotti is not wide enough to produce sounds from sources several feet apart- unless he is running about the stage while singing!
The key factor to remember is that when you are recording a song, you are either making a record, for your own purposes, of the way you
performed that song, or you are making a RECORDING. It's the difference between a snapshot and a portrait photograph for public viewing.
The rules are different.
Cheers
Dave