The four major reasons I refer to specialists are (in descending order by frequency):
1) For a specific procedure that I don't do (e.g., colonoscopy, EGD, nasopharyngoscopy, cardiac cath., etc.)
2) To cover my ass (happens more often than it should).
3) To manage a condition that I don't treat (e.g., fracture, schizophrenia, hyperthyroidism, RA, sleep apnea, cancer, etc.)
4) For a second opinion on something straightforward because the patient doesn't take my word for it (see
@smq123's previous post).