Customer-facing jobs can be nerve-wracking. Many customers only approach you if they have an issue, and one interaction can ruin your day. On top of that, you have your real name on a name tag, in the signature of an email, or on your desk.
I worked my first customer-facing job in an office a few years back and had no loyalty to the company besides my paycheck. Prior to this I had built up a reputation as a freelancer using my real name, and I used my real name at this job (Same type of work). We had so many angry customers that I was worried somehow a Karen's Yelp review could be lead back to my body of work that I did freelance that I actually cared about.
I've heard that some servers use fake names so they aren't bothered by patrons outside of work. Likewise, I do know that some job applications ask for preferred first names. But I think it would help people separate their home and work life better if using fake names at work were more accepted.