Add users on each of your sites inside the network (Multisite). If, before the installation of this plugin, a user was registered only on one of your sites, with this plugin you can add it to all of your sites and assign to all his site profiles his default (choosen) role. If no role was choosen for the user at the registration, the default role for new registered users will be used for the user. After the installation of this plugin, every further user registration will be synchronised on all your sites inside the network (Multisite).