2-Step Verification adds an additional layer of protection to your Bitly account by sending and requesting a one-time security code upon login. Whenever you log into Bitly through the website or other apps, you'll need to enter your password and a one-time security code sent to the configured mobile phone number.
With 2-Step Verification enabled - even if someone knows your username and password, they can not access your Bitly account unless they have physical control over your mobile phone.