A headshot isn't a portrait - it's an audition you mail to casting agents, directors, producers - whoever can give you a job. It has to show you in the best possible manner, it has to look like you (on a really good day, let's say), and it has to get across some of the appealing aspects of your personality. It has to have something human about it. People have to be able to look at it and sort of think they know something about you. And it also has to be striking enough that when it winds up on someone's desk it makes them stop for a moment to consider it.
There are a lot of photographers shooting headshots. What makes me different is I'm also a stage director with regional and Off-Broadway credits and I privately coach acting. I think like a director, I shoot like a director. And because I teach acting, I understand performers and how to get the best out of them.