You can moderate new BuddyPress members, fight spams, set BuddyPress groups and sites and allows new members to join them from the registration page by using BuddyPress Registration Options plugin.
Plugin’s Options Page Where You Can Turn Moderation ON-OFF and Set What Members Can Join While Registration:
BuddyPress New Member Registration Page:
If Moderation Is ON, New Members Can Login But Can Only Use Their Account After They Get Approved By The Admin:
Approve, Deny Or Block Member Requests And More:
Install and activate BuddyPress Registration Options plugin in your WordPress based website. After activation visit its settings page from your admin area Dashboard and set the options for new members to join groups and blogs from the registration page.