IIRC theymos mention about better privacy. Anyway, i don't think simply requiring to complete email verification can stop spam or scam attempt for some reasons,
1. Many temporary email website exist.
2. You could abuse plus sign on email address. For example, alt+1@gmail.com, alt+2@gmail.com, ... , alt+999@gmail.com.
3. There are some service which offer lots or "unlimited" email alias. For example, Apple's Hide My Email.