They only come in a couple lengths, there are more bike sizes than steerer lengths.

Only on one of my bikes have I cut the steerer, that one I cut it because I wanted the fork shorter for packing in the S&S case. I rode the bike for months before I finally cut it to make sure I did not cut it too short. My other bikes, I usually used a stem that was closer to horizontal to make it look a bit less odd, such as in the photos I posted above. But I think I have never had more than 20 mm of spacer above my stem on any bike so if I had a lot sticking out I probably would have cut that too.