I'm going to hop on the pro-Ejomhei and pro-rot wagon here and offer my two cents.

I took a lot of flack as a shaman for using rot, and it always bothered me. Rot is almost always a good call as a shaman, even if you don't completely nullify their regeneration/get the big rot, a failed rot still makes them vuln_disease. Trying to plague someone with decent con can be a pain in the ass, but a rot, even a failed rot, really helps with a lot of shaman supps.

It's not just meant to keep you out of commission, it has a myriad of uses for a competent shaman.