They can be good in the aspect of sending you work you may not be getting otherwise. But they also may put some conditions on you that you may not be too thrilled about as far as agreed rates, materials thresholds and Sublet markup. But that is a business decision that you may be willing to make if you need more work.
Depends on where you live, we live in a small town and drp's are great. they don't mess with us, they try to be fair, but we do too. Only real concessions we give are no storage on totals. they send us referrals, we sell the job, we fix the car, customer picks up car with smiles, they send us a check. We play middle of the road though, insurance company can't run over customer, but we won't advocate for customer getting more than they deserve either. You get respect from everyone that way.
I know in larger areas shops will try and cut their competitions throuts, which causes everyone to lose. If a couple of shops agree to anything, an insurer thinks its the norm and everyone ends up suffering.