As a bike rider myself I like to cut through the taffic coming up to lights for 2 reasons. 1. avoid idiots lane changing without using mirrors or indicators. 2. because I can!!! Who wan'ts to be stuck behind a whole heap of traffic if you can help it. (I don't ride through moving traffic, thats asking for trouble)
As for setting off quick, if there are 2 lanes and you are in the middle, you need to decide which lane you want to be in and get there quick. If a car tries to race you then good luck to them. Would have to be some seriously quick shit.