I'm confused. What are the major pros/cons between HERMS and RIMS brewing systems? I've read about both, but can't seem to come to a conclusion on why one would choose one over the other. Is it the amount of fine-grained control the brewer has over the process, simplicity, equipment or quality of the beer? Like most things, I'm guessing that it's a matter of tradeoffs, but as someone who is thinking about going all-grain, I'd like to understand the tradeoffs better before I make a decision to invest in any equipment or implement a new process.
A RIMS (Recirculating Infusion Mash System) passes the wort directly over a heating element to achieve temp changes. A HERMS (Heat Exchange Recirculating Mash System) passes the wort through a coll submerged in water to do the same thing. Although temp steps may be a bit slower, you don't have the risk of scorching that you do in a RIMS. Probably 90+% of beers can be made with a single infusion, but if you really want to do a step mash they'll (somewhat) simplify the process. Neither system is necessary for making great beer, but if you have the $$ and the urge, go for it.
Your question was RIMS or HERMS, but I agree that for someone thinking about going all grain, it should be, maybe, simple insulated mash tun, RIMS, or HERMS. But sticking with your original either/or question...
The biggest difference to me would be the amount of caramelization; if you pass wort over a really hot heating element, it might have a carmelization effect (to the point of scorching, as Denny said), whereas if you passed wort through a heat exchanger that was (at the hottest), just barely over your target mash temp, then you would get less carmelization, and no risk of scorching. That's not to say you can never avoid carmelization with RIMS; a decent rate of flow, and not too much energy on your element, you'd be fine.