Hi Mark,
You can have just one role and keep adding users as needed but the content is not tailored to the users or the roles, it would be the same content for all users in the role, the content doe snot change according to roles or users, if you need something like that you would have to implement a custom feature that adapts according to the user id or something.
If you need different content instances per user then you should use a role per user even though it creates a lot of roles.
What I hope to be able to do at some point is make role management less unwieldy even when there are lots and lots of roles.
Best,
Joe