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.
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 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.