PT Lover answered it for me - thanks! I remember the first time somebody showed me that feature back in the 4.x days, I think it was. Or 5.x? Can't remember. Anyway, what a revelation! I've felt like a kid with a new toy ever since!
As to mixing in the box start to finish - eh - whatever works for you. I say use both tools to their strengths. If you have a board that does really good analog summing, it can do some lovely things for the sound that digital mixers can only vaguely emulate, I don't care what plug-ins are used.
The repeatability of automation is nice but once you start messing around with fudging automation breakpoints with your mouse and such, things can quickly start to lose musicality. If your board is one of those lovely old all-discrete, high-voltage babies, I would be very reluctant to entirely give up sending out to it, if I were you.