Default comment visibility?
When a support agent is making a comment/reply to a topic, the default visibility is public. You have to remember to change it before you post, or else the author will be notified. In some support situations, there are far more internal/private comments than public. It could create problems if a support agent thought that s/he were making a private comment, but forgot to change the visibility to "support agents". It would be much safer to default to "support agents" and then have the option to change it to public.
Is there a forum setting (or support agent preference) that will default all comments/replies to private (i.e. "Support Agents")?
We personally use "private comments" and we never had such situation. Most of the time when you post a comment you answer to the user. So, It is public for most cases. Also we had no any complaints from other customers about it.
But, anyway, we will consider this as a settings if you really want it. Personally I think this will add more actions to your agents' routine (change status each time).