The only time I've tried to use the 2 or 2.5 was when my wife complained that her brake lever reach was too far out. Multi tools are too bulky to reach into the reach-adjust screw so there was nothing I could do (and let that be a lesson to her, check that crap out before you hit the trail). V-brake spring tension is easy to adjust without any tools, just bend the spring.
I had a friend who's crank arm came loose during a ride so an 8mm would have been useful for him. But really, how often does that happen? And today a lot of crank bolts are bigger than 8mm.