I like when specialists call me to discuss a case prior to doing something off the wall. Usually, it's an oral surgeon to talk to me about aesthetic concerns for an anterior implant. Like I had a patient with a severe bony defect on #9 and the surgeon called to say he didn't think an implant would work due to the location of the bone. So we ended up doing a partial. Another time he called me to say he could only do a really angled implant on the anterior. The patient was deadset on an implant. So I talked to the restorative lab and we were able to develop a restorative plan to account for the angled implant. It went well and it's still in service years later. I've referred a patient to endo for 1 endo and sometimes, they'll need more. The endodontist I work with will usually call me and let me know what the patient needs.
As for the bad, I once sent a patient for a perio consult for grafting and they returned with a newly restored implant on a tooth that needed endo and the grafting wasn't done. I have one periodontist that patients will occasionally find and he'll send the patient back to me for me to complete the same procedure (SRPs, splinting, osseus sugery) I referred for. If I refer for procedure, it's because I don't feel comfortable doing it.
And no reports being sent is the biggest problem for me. My favorite game is playing "guess the implant" because the patient doesn't remember who did it and I never got a report from the specialist. If the patient raves about how amazing you are, I can't send you more patients if I don't know who you are. I've had a few patients find a surgeon near me (for implants or extractions) and said how amazing the office was, the doctor was fantastic, etc. They always forget this name. I have no idea who he is because I've never, ever gotten a report. So, I can't send him more patients. There's also an ortho like this. Beautiful results, great occlusion, happy patients. No idea who they are because no report and patients don't remember who they're seeing. Always, always send a report.