Withdrawing from one of more classes could affect your financial aid in two ways. First, a reduction in hours could create a balance due on your account. This results when a student has not completed at least 60% of the semester, the point at which all aid is deemed as "earned".
Withdrawing from courses could also affect your financial aid eligibility with regard to your Satisfactory Academic Progress. You are required to complete at least 67% of all courses attempted, so multiple withdrawals will quickly make any student ineligible for financial aid.