When I was building our house I wanted a 3-4 car Garage, but was out voted by my wife, with the logic of we only have 2 cars why have so many other stalls, my plan of course was to expand our vehicle line up. I tried to argue her same point with bedrooms, we only had 2 kids why build 5 bedrooms?
Well 6 years later we have 2 pick-up trucks, 2 cars, and 2 motorcycles. In the summer time her Mercedes SLK convertable lives outside, so that our bikes can live in the garage, winter time her car is allowed back into the garage, because I put the bikes in the bar room in the basement(this makes working on them even more fun, I get to watch football, drink beer, and wrench on the bikes all in one place).
By the way we ended up with one more kid right when we moved into the house so now we only have 2 empty bedrooms. I'd much rather have 2 more garage stalls since I've expanded our vehicle family faster then our family.