Quora has bots that do a lot of moderation, such as: auto-question-tagging, marking questions as "needs improvement," auto-question-merging, auto-answer-collapsing, and even auto-question-editing (like grammar/spelling correction). If bots like these were implemented on Stack Exchange, would they make communities better, or are they unnecessary?
A lot of moderation is already done automatically; the fact that there aren't specific user-visible "bots" that do the automated moderation is besides the point...
There are already auto-flags raised for content quality, there are auto-flags raised for things like excessive numbers of comments, user activity (e.g. for mass deleting content) and probably a bunch of others I can't remember or don't know about. Questions are automatically protected if they are the target of low-quality answers, posts are automatically bumped if they meet certain conditions, tags are automatically removed if they are unused... and probably a lot more, those are just the first things that come to mind.
Automated processes that need to be associated with a user are attributed to the Community user, which essentially is a bot that does a lot of moderation (or at least the public facing attribution for the automated moderation that happens; I'm not sure about the internal mechanics).
There are also a lot of community created bots that help with moderation. See for example, SmokeDetector (which helps detect spam posts), Charcoal (which runs SmokeDetector) and SOBotics (A SO chat room for testing moderation bots).
So yes, bots can be useful and beneficial... and a lot already exist.
Some related reading:
- Are bots specifically allowed or prohibited in Stack Exchange chatrooms?
- Should we have special accounts for bots?
- Present and future of bots on Stack Exchange
- Has anyone ever tried running an answer bot on Stack Overflow?
- How should a bot earn enough reputation to perform the actions necessary for that bot?