You will have instances when someone either:
1 Enters their sign up details with no intention of really signing up
2 Enters their signup details with the intention of signing up, but changes their mind.
This will be unassigned data. In either case, the email address cannot be used again until it is cleared.
So, you may wish to:
1 Clear a member quickly so they can try again
2 Resend someone a payment link to continue their signup
Both of these options are available via the 'Unassigned Members' section. The latter via the 'Contact' option.
Please see the
members docs for some of the functions.