It is highly recommended to use this option. I also highly recommend to enable 2FA for your email account that is associated with your bitcointalk account. I would enable 2FA for every important account where possible. It's not the magic bullet, but makes stealing accounts way harder.
Activate 2FA for email account is important for the forum account security.
If an account was registered with a non-existing email, it's time for change. Read theymos' advice on it. It's possible to use non existing email address to register an account, but in security, it's bad.
If you don't want to set an email address, use something like yourUserName@invalid.bitcointalk.org; don't use a random nonsense email like y@x.com, since somebody might create that domain/email.
Because your old email didn't exist, somebody could've registered your non-existent email address and used that to steal your account.