Yeah it's great - especially if you've got multiple machines to work with, but even if you don't. We had a render that was going to take 8 hours on one machine -- threw it on all of our machine on Render Garden and it was done in 20 minutes.
If you’re not using render garden to create your intermediates you’re wasting time. 90% of my work requires a DI so 90% of my comps are rendered through RG.
I also use it to render off an MP4 send proofs to clients. As Rob said it’s a tremendous timesaver. You never have to wait for a renter to start working on the next cIMO.