When Confluence gives the Use permissions for anonymous in Confluence, it will let any anonymous edit or create content in the instance. However, when an anonymous is creating content or editing a page, the following message is presented:

The reason for asking to modify this message would be regarding. Companies that allow only employees to have login in the instance. Otherwise, if the anonymous user is not aware about it, he could send messages to the administrator to ask for a login. Depending on the number of anonymous, it could need some extra work.

A good suggestion would be to remove the login link for anonymous user in that message.