Asking xiaobaitu and others regarding 485 ref

more people have to Ref before their i-485 got approved. my questions are:
1. when uscis officer need 485 ref, what kind of documents do they normally ask ?
2. is that ture that if you used/applied i-131 and EAD , most likely you will be asked for i-485 ref before your GC got approved ?

thanks