P.R. Rules at China

My American husband is an employee of US company, who is a vice president and holding a F currently at there. He stays at Beijing 3weeks /monthly for the past two and half years.
Why is he applying for Green card now? Is it better to hold PR than F? What is the advantage to do so?is the new immigration laws that they had just announced requesting the certain business foreigners to follow through this regulations?any taxation reason? Thanks.