It suddenly hit me because one of my guitar students is just starting to learn bar chords, and she keeps trying to support her 1st finger with her 2nd. A lot of beginners do that, but quickly learn that in a lot of bar chords, they're going to need that 2nd finger somewhere else. It's just a matter of time and practice, building up strength in the barring finger.

I don't see that as something you shouldn't do for that one chord formation. I do it, when I'm using an Em formation at a higher fret. Most barre chords, you need all three of the other fingers elsewhere. Em, you have a finger to spare, but you're holding 4 strings down with the barre, not 3, so you need to put a little more pressure on the barre. So why not?

Peter.