Depends on the nature of the thread.

I have one that was set up with a lot of elements that required frequent management (since certain things were more like a game). Eventually when I had 18 active roleplayers I got super overwhelmed doing all of that management myself (we used dice for determining random encounters with creatures and a few other things and it was getting to 200+ rolls a week sometimes).

However, I feel if I had people who were capable of taking on some of that for me, I could have probably continued on with it without getting super burned out. I've since said when it is rebooted I am limiting the player count to 8 until I get someone I feel is capable of assisting with managing it.