During self-enrollment, students only enter their e-mail address once. I have had several students make a small but important mistake (forgetting a letter, adding a letter, etc...) and then they can no longer access their course on future log in attempts. Sometimes they even create new accounts which causes additional issues.
I think it would be useful to have the option to force students to enter their e-mails twice when they self-enroll/register and have a mechanism that confirms they match. This would cut down on the number of incorrect registrations.