One disadvantage of tuition reimbursement is that you typically need to pay for your classes upfront, then submit the bill to your company for reimbursement. Some tuition reimbursement programs also have strict requirements and limitations, such as a cap on the amount of money that can be reimbursed, or only covering certain types of courses or degrees.
Also keep in mind that balancing work and courses can also be challenging for some employees to manage successfully.