Further to that, you (as the community) can also help clean up comments on posts by flagging them or removing your own stale comments as you come across them.
From the How do comment voting and flagging work? FAQ:
If a comment is flagged by enough users it will be auto-soft-deleted. There is no penalty for this. Flagged comments will be surfaced to moderators, so if you have a problem with a comment, flag it.
You can always delete your own comments by clicking on the ⊗ that appears when you hover the mouse over the"Delete" link next to your comment. This is not a flag, it takes effect immediately.
Comment flags do not affect the user in any way if a comment gets deleted.
Flag a comment by clicking on the flag icon that appears when you hover the mouse over the comment. You'll need to enter a reason (see below).