For instance, it's a pretty sure bet that I will never get cast as the evil antagonist, the alluring femme fatale, or the bossy executive. Right now I'm getting cast mostly as a teenager, and usually as the girl-next-door type. That's what my face and my voice and my delivery says to casting directors. For me to audition for characters far removed from that type isn't a good use of my time, as it's very unlikely to produce results.
It's important to know your type, and to market yourself as that type through your headshot, your website, your demo reel, etc., because that is your BEST SHOT at getting cast in a film. Granted, once you start booking a lot of roles and building your resume, you may have opportunities to expand past your type.
This is a great article to help you figure out what your type is: 4 Ways to Nail Down Your Type.
I like this quote from the end of the article: