Personally, sometimes I'm going to say things that are against the industry or specifically the actions of the company I work for. If my real name was shown someone could connect me to the actual business and they'd see me as some disloyal employee and not only would I not have a job, I could be blackballed by the industry because most businesses follow the same practices.
With this level of anonymity I can post my opinion about these subjects and not be calling out an individual company or connect the comment to myself in order to alienate myself from other potential employers.