The c hub lowers the roll center. shaving the u-brace and mounting the ball stud lower raises it back up. The theory is that lowering the link in general makes for different roll center behavior, even with the roll center starting locations can be adjusted the same as A hubs and a normal brace.

In general, people shave their brace and go to a c hub at the same time, but using A or B hubs with a shaved brace is also a very valid tuning option, allowing for a significantly higher roll center. I run A hubs with shaved brace and 2 washers with green rear springs at my track -- this is what works at my track. White springs on a higher bite surface are typically paired with c hubs and a shaved brace followed up by ballstud tuning at the inside brace.

Run what works, don't be afraid to experiment.