For chat flags, the only guidance the spam/offensive-flag dialog provides is the following:
Do you want to flag this message as spam, inappropriate or offensive?
From the amount of disagreement and discussions about chat flags I've observed and participated in I'm convinced that this is just not enough guidance for the users on what exactly they should be flagging.
The additional complication for chat flags is that successful flags result in an automatic 30 minute suspension. This suspension is certainly appropriate for certain behaviour that results in flags, but I personally don't think it's appropriate in many of the common cases that are flagged.
The flagging dialog should provide a predefined list of reasons for flagging, like the dialog on the main site does, and adjust the consequences based on the choice the users make in that dialog. My hope for such a change would be that it would help to establish common guidelines for chat moderation across the different SE sites and that it would avoid suspensions in cases where they are just not necessary.
The distinction I'd draw is between flags that should result in suspensions and those that should only delete the message, but not suspend the user.
The case where I think an automatic suspension (and probably even more severe actions) are necessary are direct insults of other users and deliberate disruptive behaviour.
Where I don't see any reason for suspensions is e.g. inappropriate language, as long as it's not intentionally disruptive.
So I'd imagine a dialog like this:
is insulting other users or deliberately disrupting others (includes automatic suspension for x minutes)
contains inappropriate language according to [insert link to policy here]
some other reasons I can't think of at the moment
The actual text of the reasons certainly deserves some debate, as far as I can tell there is no real consensus on which posts should be flagged. Explicitly mentioning the reasons for which flags are appropriate might help to make chat moderation less random and reduce the number of spurious flags.