Federal financial aid comes with lots of strings attached. To continue receiving federal financial aid the US Department of Education requires students make satisfactory academic progress toward the completion of their degree/certificate. Also, there are limits to how much aid a student can receive under certain aid programs and maximum time-frames in which students must complete their degrees or forfeit aid eligibility.
The number of credits a student attempts in a given term can affect the amount of aid for which they are eligible. Dropping classes or withdrawing from school may result in aid needing to be repaid which can also adversely affect a student's ability to progress toward the completion of their degree.