My thought for bow placement is mostly determined by the tone color I want for the music. In orchestra I usually need a warmer and rounder sound so I play closer to the fingerboard, this is also because my bass is a bit on the bright side. For solo work I tend to play much closer to the bridge since I want a more focused and projecting sound. As for practice I tend to work with my technical work (scales and such) close to the bridge since it is harder to play and I need to practice the hard stuff
