I was recently notified that another moderator on the site had suspended a specific user. I followed this to the source, but found some edited comments. My colleague had removed the offending parts from the comments. While I know that the suspension was justified in this case based on other information, I find it a bit problematic that such moderator actions can't be followed easily.
Moderators are all CCed on suspensions, this helps to keep informed about problematic stuff that happened on the site, and serves as a way to check the actions of an individual moderator. But this doesn't really work when comments are edited, as we can't see the old versions without help from an SE employee.
This is one reason why I personally never edit comments in such a way, but instead just remove them entirely. This sometimes removes valid information as well, so it is not without drawbacks.
While this isn't needed very often, I think it would be useful if moderator could see the edit history of comments edited by moderators. This would bring editing comments on the same level of transparency as other moderator actions.