Depends on the sort of system, really. I myself try and follow something akin to having the audio path and modulation sources separate, with the audio going from left (oscillators) to right (filters, post-VCF VCAs, etc), and then loading the modulation sources in in groups, but so that the control signals go upward and on the left, and the audio goes downward and on the right to the output module(s). But there are "special circumstances" where this might not be the best solution.