i didn't think it was legal? i guess it depends state to state. or maybe it's just that i've always worked with ethical people.
there is occasionally good reason- we've done it on cats who were so debilitated, emaciated, and dehydrated that it wasn't possible to find a viable vein, but those cats were masked down to unconsciousness with gas anesthesia first. i've done it with my rats, but again, they're masked down first.
for healthy dogs? there is no good reason. if you can't hit a vein, you shouldn't be there. and that's not even touching the subject of whether these dogs should be pts.