I don't know, it probably doesn't make a lot of difference, but I've always thought that with a pan under it, it would slow the smoke penetration down. On smaller cuts, I do it sooner, just like it to get full force of the smoke under it until it gets up to temp.
Surprisingly enough, this thing hasn't release much juice at all since I started it. The water pan didn't have much last night, and there isn't hardly anything in the foil pan. Figure when it hits 170 and I foil it, I may see some then.
I like the crispy edge on my brisket even when it's sliced. I'd guess you would get some of this if you sear it, so you wouldn't need the rub that way. I may try that next time.