The SCLogin module has an option for "Show Connect Account Button(s)". When you enable that, and a user is logged in, the social network icons will show for networks that the user hasn't already 'connected' with.
With that, when a user is logged in, they can connect their Joomla account to more social networks.
Other options are to enable the "Automatically link users by email" setting. With that, when a user logs in with Facebook or Google, if their email address already exists in Joomla, the accounts will be automatically linked together.
The final option is to disable Automatic registration and set the Registration component to JFBConnect. Then, when a user tries to login with a social network for the first time, they can choose to sign in with their existing Joomla account.
Those are the options available. Hopefully that gives you some good ideas on what may work best on your site.
Thanks,
Alex
Login Workflow JBC Best Practices
