A professional headshot is an opportunity to portray yourself to casting directors, producers, agents, and managers. You want to show what you look like, what kind of roles you can play, and what kind of variety you are capable of.
Your headshot is meant to exhibit the version of yourself that will convince agents, casting directors, and everyone else that you deserve the job.
Actors behave truthfully under imaginary circumstances. An honest headshot is a good first step in that endeavor.