You have the option of turning off the registration for the plugin. There are two potential uses for this setting.
Managing Registration Elsewhere
For users that might have some other method of registration, up to and including private blogs that don’t want anyone registering and thus sending invited users login information. In this case, turn off registration and do not establish a registration page.
Removing Registration From Content
The process flow that WP-Members™ uses by default is the assumption that minimal clicks results in increased registrations. Simply put, if an unregistered user ends up on a page that requires login and registration, they are presented with a login form (in case they are already registered but haven’t logged in) and a registration form (so they can register right then and there, without leaving the page and having a chance to change their mind).
To make the plugin as flexible as possible, turning off the registration will remove this registration form from the inline content areas. In this case, it is advised that you specify a registration page to direct users to.
This is not the same as turning off registration for WordPress itself. That is a separate issue. This is simply a setting to remove the registration from from the blocked content area.