A lot. Your pdoc is the only one who can legally diagnose you with a medical condition that precludes you from work and therefore qualifies you for SSDI. If your pdoc told you straight out that he didn't think that you could hold a job, that's what he's going to report to Social Security, and you should reasonably expect to receive disability benefits. If for some reason you are denied benefits, this pdoc's opinion should be grounds for an appeal.