I've always had an easy time with math so admittedly I think sometimes it's quicker for me to just to do a quick calculation, but if I am remembering correctly it really helped me to keep more complex conversions straight, especially when dealing with square units, etc.
I really hope I'm thinking of the right thing, and dimensional analysis is the thing where you line up conversions in a table looking thing.
ETA: This is what I was talking about
:
http://www.alysion.org/dimensional/fun.htm only it wasn't on quite as simplistic of a level, and it really didn't have to do with how many pizzas I needed for my pizza party, haha.