And at only $600 (+ $250 a year) RenderMan is comfortably within the budget of serious hobbyists and budding freelancers.

I'm not in a position to make a comparison, but I think a big drawback of cycles is it's very noisy. It's one of those things where you maybe get an OK looking render in 30s, but it takes >5m to get a render that's actually noise free. Which is workable for still frames, but painful for animation.

For hobbysists? Likely not much, other than familiarity with an industry standard renderer (though not as popular as it once was).

For professionals, you get quite a few things but speed optimizations (resolves faster in my experience), render quality (usually fewer fireflies in my experience) and some more advanced transmission models to name just a few.