While the High Tek coated bullets (most common coating used by commercial casters) does keep the bore very clean, it tends to deposit a really hard layer of plastic/carbon/crud inside silencers or muzzle brakes. This type of deposit seems to be much harder to remove than if you were to just shoot lubed lead through the can. I got one can crudded up to the point I didn't feel safe continuing to shoot it.
So I did a test, using a muzzle brake with a removable endcap which I could weigh before and after to get a deposit weight.
I found going to a slightly oversized bullet decreased deposits significantly. But switching to a copper plated bullet dropped deposits to virtually none.
So while I still use a lot of coated bullets for USPSA or general shooting, I stick with copper plated or jacketed for suppressor use.
Full write-up
Here.