Email verification allows for someone to not make hundreds of accounts with ease, deals with spam prevention at the best possible way, and allows for users to be able to feel more secure (I can send out newletters, updates, etc. since I have their address on file that I would not be able to do otherwise). If I register for a forum and they don't care about my email verification (or another method of personal information), I get very skeptical of it right away.
I still get some auto registration even after I set it to email verification for new members. When started a new forum there were over hundred members register to my forum and later I realized they are not genuine people coming to post but all they have adult posts and selling some products.
