If you are running a multi user WordPress installation it might get tricky to notify all existing users of an important change or bring new users up to speed on rules and procedures on the site. Luckily there is a plugin for this.
This small plugin allows you to create global announcements. Once a user logs in they will see you announcement in their dashboard before anything else. You can also set them to be mandatory and the user will have to tick a certain box stating they have read and understood the announcement presented to them, otherwise they will not be able to proceed on the dashboard. This way you can make sure all logged in users get any important information you need to pass to them and new users have T.O.S. readily accessible when they log in on the dashboard, along with any other on-boarding info.