One reason is that if you accidentally deleted a client's account you can get it back. Another reason is that it allows only one account per email - say you removed the user for whatever reason, they can not use the same email to re-signup or make duplicate accounts.
There are more pro's then con's on this issue. But as I said, we are planning to revisit this situation in a future release.
There are more pro's then con's on this issue. But as I said, we are planning to revisit this situation in a future release.