Whether the agreement on signing and returning the top car is useful depends on the specific situation and the specific content of the agreement. If the agreement is signed by both parties voluntarily and conforms to the law, it will have legal effect. However, if there is fraud, false promise or violation of legal provisions, it may be invalid.

Generally speaking, the waiver agreement can be regarded as a contract, which stipulates the rights and obligations of both parties. If the agreement stipulates that one party is exempted from repayment responsibility, it has legal effect. However, if there are other clauses in the agreement, such as requiring one party to bear the ownership and use risks of the vehicle, whether these clauses are effective or not needs to be judged according to the specific circumstances.

Before signing the exemption agreement, it is recommended to read the agreement carefully and consult a professional lawyer. Lawyers can help you evaluate the legality and validity of the agreement and provide relevant legal advice.

To sum up, it depends on the specific situation and the specific content of the agreement whether it is useful or not. Before signing the agreement, it is recommended to read carefully and consult a professional lawyer to ensure that your rights and interests are protected.

Legal basis:

Article 44 of the Contract Law of People's Republic of China (PRC) stipulates: "A contract established according to law shall take effect upon its establishment."

Article 52 of the Contract Law of People's Republic of China (PRC) stipulates: "A contract is invalid under any of the following circumstances: (1) One party concludes a contract by fraud or coercion, which harms the interests of the state; (2) Malicious collusion that harms the interests of the state, the collective or a third party; (3) Covering up illegal purposes in a legal form; (4) damaging the public interest; (5) Violating the mandatory provisions of laws and administrative regulations. "