Most users who find your website from search engines will most likely never find your website again. Email subscriptions allow you to convert those users into subscribers.
This way your users will get the content delivered to their inbox. It helps you build a loyal audience that keeps coming back.
Formidable Pro allows an easy way to create a form that can be used to collect contact information, but there are many email service providers that provide their own plugins. Take a look at MailPoet, MailChimp, Aweber, AgileCRM, and ConstantContact.