How useful is it for lawyers to apply for disapproval of arrest?

It's huge. According to Article 86 of the Criminal Procedure Law of People's Republic of China (PRC), the people's procuratorate may question witnesses and other participants in the proceedings and listen to the opinions of defense lawyers when examining and approving the arrest. However, if the defense lawyer wants to put forward the opinion of not approving the arrest, it should be after the public security submits the opinion of approving the arrest and before the procuratorate makes a decision on whether to approve the arrest.