Hi - the capabilities you seek are commonly found in something called a finite capacity planner. WorkFront is an infinite capacity planner. There are no constraints on resource assignment possible within WorkFront.
The best I think you can do is look at the user utilization to identify the over-allocations, and then you choose the project (lower priority) and then adjust the task duration (to reduce the daily demand), adjust the hours assigned to the resource (to reduce the daily demand), or change the start date of the task (to push the demand out).
You have to resource load level the old fashioned way.
Let me know if this doesn't answer your question please.
Thanks, Eric