There might be many reasons why your need your own digital identity. Digital identity in terms of your blog or site representing as you in the entire cyberspace. If you have a WordPress blog or site, you can use the URL of your blog as a digital identity, the usage might be many including OpenID appreciation which allows you to log in to sites that support OpenID. Basically, OpenID is an open standard that allows users to authenticate to websites without having to create a new password.
Digital identity is a psychological identity that prevails in the domains of cyberspace, and is defined as a set of data that uniquely describes a person or a thing (sometimes referred to as subject or entity) and contains information about the subject’s relationships to other entities ~ Wikipedia