I never crop if I will contact print.

I always try to compose full frame with 4x5 but due to limitations of the lens or compromise on my spot in relation to the scene it may be unaviodable. That being said, I am composing on the ground glass with that in mind and not going into the darkroom later and saying "gee I didn't see that, I'll have to crop it out."

For some reason it is hit and miss with 35mm. I don't know if due to using LF I have a hard time being precise with a 35mm and if shooting from a tripod i usually compose to not crop, but shooting handheld, regardless of how carefull I am I sometimes need to crop some thing out later.