Yep with the DLC that allows you to make skills Legendary (reset them back to 15 and get your perks back), leveling up is supposed to be almost unlimited.
Mr. Irishman is right. It depends on the skill being mastered. But there is sometimes a really good reward, like for enchanting.
Also, keep in mind, then once you get above skill level 90 in any school of magic, you now have the potential to do a quest and get the Masterspell(s). Those are the rewards for mastering schools of magic.
Really, though, you don't have to master anything if you don't want to. For example, I don't take my characters overly far typically, and when I use archery, I've NEVER gotten over skill 80 in it. That doesn't stop me from killing everything. With smithing, you can get other armor to the cap, so you don't have to use dragonscale or dragonbone. Some masterspells ended up being worthless to me. It's just a matter of preference, it can make your life easier sometimes though.