I ran a bare bottom for 4 years. Only downside I saw was (personal preference) aesthetics because I like sand. Another was I had to keep hidden sand reservoirs I made from live rock so I could keep certain kinds of wrasse. Other than that...
BB was really easy to clean. All the dirt found it's way into the area with least flow and made it really easy to siphon it out. And my phosphates and nitrates were always easy to control. Instead of sand I had montis, chalice, and zoos growing on the bottom.
...thinking about it... why do I have sand in my new build? Haha