well, technically, you should be able to sing anywhere - then you're working on your strengths and weaknesses (and eliminating your weaknesses, whic hcan only be a good thing!).
If you always tend to stand next to the same people, you will never improve, and it'll be harder when suddenly they're not there, or you're on your own for some reason.
I did fall fowl of that trap quite a few times, and found that it took me a long time to be confident in my own voice.
I noticed it a lot in the other singers too.
In our choir, it's much, much better not to stand next to a specific person too often.
we have an ex-professional singer who when she messes up, so does everyone else, regardless of how well they know the piece,
a tenor who cannot sing his own part - always deviates to the treble line when singing in harmony (not even following his own rhythm!),
another tenor who is brilliant, but has recently left us, meaning the other tenors are left floundering (ie they daren't sing stuff even that they know, especially exposed parts)
other sopranos who sing rather quietly, and when the afore-mentioned sop isn't there, it sounds like they daren't sing anything.
then you've got me, who is really unsure of her voice, and thinks it sounds dreadful, but has to sing up to encourage the others to sing a bit more self-suredly, and ends up being the loudest on the recording 
(which is fine when I get it right, but when I get it wrong )
so, yep, I subscribe to the practice of moving around regularly to help your own strengths and weaknesses .
John Bertalot suggests this very strongly in his books, too.