As you may be aware there is a team for every business unit including the root business unit and when you add a new user it automatically becomes a member of this team. So by applying a security role to the root business unit team every user will have this role. In the example below I copied an existing security role and renamed it as the “Default Security Role”. I then applied this security role to the root business unit team so it will be applied to every user.
Now when you add a new user you no longer need to give them a security role as they will automatically get the default security role. The only thing you need to careful of is that you set the security roles at business unit level as a minimum. Setting them at user level will not work.