PROS: Faster sorting (no unrolling), ease of transport (bags are sturdy and have handles), initial access to grandma's collection getting dumped rather than waiting for it to circulate through the coin services.
CONS: Some machines reject silver so dime/quarter bags may be useless. Once you build the relationship with the bank its tough to back off if its a weak supply, you lose credibility. Increased dumping. Potential of bag being short. You don't get rolls to re-wrap your dumps so now you are dumping loose in machines which means additional risk of getting shorted when dumping (specific to dimes)
Traditional silver (halves, quarters, dimes) I do boxes. Don't have access to a machine that doesn't reject silver.
Base coinage, bags are ideal. I am pulling ~28% Cu from my pennies and ~60 pre-60's/2 war nicks/1 dateless buffalo out of every bag.
I agree with one of the earlier responders, try pulling a few and see what you get, make a determination after 3-4 weeks of pulling bags from there.