Careful, and often quick, composing is a skill that comes with practice. There are times when it's impossible to get the composition just right in the camera. When out in the field, extenuating circumstances impose limits. So the best one can do is get the composition as close as possible and realize it will be necessary to crop. Now that I no longer have a view camera nor a tilt-shift lens, I often have to shoot a scene a bit wider than I'd like so that I'll be able to compensate for the keystone effect in post. My stylistic tendency is to keep the geometry true.