Underwriting - Experienced agents know how to handle impaired risks, both from the submission end as well as the delivery of substandard policies. Good agents know how to prepare prospective insureds for exams and other requirements, and they also have established relationships with the services that perform the exams. To give you an idea, a 45 year old 250 lb. This is NOT an area where you want to screw up. This business really isn't for amateurs and you can't learn it from a book, so you need field training.
Joint work is the best way to learn.
In both career and brokerage, I've witnessed too many people fall on their face because of greed. I've seen it happen. If they've done some good work but not a complete job, then I offer to split business with them. Some refuse and try to keep it all. I'm shamlessly guilty of robbing business from these greedy amateurs.