For the most part CG's are fun and a diversion from the normal grind of the game, but why do you take part in them?
Personally in the past I took part in CG's because it was a decent boots to my income at the 40% level, but after getting a Type 9 in addition to my Python they are for the most part a waste of time.
At a high paying trade CG the top 5% is occupied by CMDR's often trading 12-20k+ worth of commodities to forward the goal and earn 18 million credits or so as a reward. In a Type-9 that is 24-40 round trips to the turn in and on a normal trade rout that would earn 21-35 million. So what is the draw or allure?
Edit: CMDR Arda was nice enough to link some interesting information here that lends credence to the C rank tier of 40% being the way to go if you are simply concerened with maximizing profit.