I've always run rim brakes. To get the best performance out of 'em, I'm fastidious about truing, so that I can get the pads as close to the rim (less "play") as possible. I use the pads as a truing guide.

With discs, there'd be no need to true for brake function...and I'd have to pop the wheel off and put it on a truing stand each time...

Seems to me that the combo of "rim brakes+true wheels" > "discs+wheels trued 'whenever I get around to it'."