I pre-twist mostly because its the I learned many years ago, too many to really say, and I will always pre-twist until I give up this crazey trade. What it really comes down to is we do it the way we were told to or learned in some type of school. If it works for you, great, no matter what is said here people will not change pre-twisting or the type of box they use, they all work and are code legal. I hope I didn'n step on anybodies toes with this statement, but when I teach code classes and this comes up I tell the students the way I do and why, but out in the field to listen to there boss.
Lou