1. There are conflicts of interest between defendants: in the same criminal case, different defendants often have choices in criminal status, role, causal relationship determination and so on. This feature of checks and balances directly affects the severity of each defendant's punishment, so the interests of each defendant are not fundamentally the same.
2. There are conflicts of interest between lawyers in the same law firm: there are often competitive or cooperative relationships between lawyers in the same law firm, which will inadvertently mix lawyers' personal feelings into the case, which is not conducive to fully and effectively safeguarding the legitimate rights and interests of the parties, nor does it conform to the provisions of the Lawyers Law that "lawyers shall not represent legal affairs with conflicts of interest with themselves".
3. The defendants may collude with each other: when different defendants in the same case entrust lawyers from the same law firm to defend them, the communication between lawyers at work becomes a bridge between accomplices. When the lawyer inadvertently reveals to the client the confessions of other accomplices he knows, it provides conditions for the defendant to adjust the confession.
4. The defense business of multiple defendants in the same case is arranged by the same law, which is not conducive to the orderly competition of law firms, to maintaining the seriousness of justice, and to the public's recognition of the fairness of the proceedings and conscious acceptance of the verdict.