Since you're here, you probably have an account already.

Adding an email address to your account is a great idea. If you ever forget your Wikipedia password, you can have it emailed to you — but only if you add your email address to your account and reply to the confirmation email!

Adding an email address also allows other editors to contact you, and you can get email notifications whenever pages you're interested in are changed. Your email address is not revealed when other users contact you.