What cjoseph was trying to explain is that it could be very confusing to troubleshoot an issue when both are applied.
Using the bandwidth contract gives you the ability to rate limit per user or per role but the traffic management gets applied per VAP/RF Band if you have several VAPs applied under your AP-Group .
He suggested just using the bandwidth contract under the user-role will be more effective but of course it will depend on what you are trying to do.
What are you trying to do?