If the current user is a licensed user of Sage 50, this checkbox will be checked. Users who are not licensed will not have access to the Sage 50 program, so every user that you want to grant access must be licensed. If you want to unlicense a user at any time—to license another user instead, for example—just uncheck the Licensed box.
When you start granting new users security and access rights, Sage 50 will automatically license as many users as you have licenses for. For example, if you have five licenses according to your agreement, Sage 50 will automatically license the first five users for which you set up security/access rights.