When the quicks weren't doing well, he'd bowl more overs than anyone. That's a bit more than Stokes/Wood/Archer will ever be allowed to do.
Having a spinner who can do that as well as attack (eg last over before lunch, 4th innings on a wearing pitch, India) is quite helpful. Still, Bess was relatively economical even when he wasn't taking wickets last test, wasn't he?
We used to go into test with Branderson, Bres and Swann. If we didn't bowl them out for under 200, Swann had to bowl a lot of overs.