One of the hardest conversions is getting new users to register for a website. A sign-up form is the single greatest turn-off to potential users.Having to re-submit the same personal details and create new user-name/password combinations is a tedious process and one that users avoid whenever possible.
Most users tend to use similar usernames and passwords between multiple sites. But obstacles like site-specific password formats and unavailable user-names keep increasing the number of combinations that users must remember.
This hurts conversion numbers.