These days, having an actor's or director's reel is becoming an industry standard. For actors, having a reel is important because casting directions typically review reels on casting websites like hollywoodcastingandfilm.com before deciding to invite an actor to a casting session.
For directors, having a solid director's reel is important because actors often research the experience and the credibility of filmmakers and casting directors before deciding that they want to attend a casting session.
So if you're an actor, if you don't yet have a reel- what should you consider important? First, you should make it a priority to develop two different kinds of reels- a comedy reel, and a drama reel. Since the types of scenes of so wildly different in tone between comedy and drama it will be increasingly helpful to casting directors to view content that is reflective of the role you're actually audition for. And delineating the kind of work you're capable of between comedy and drama will get you invited to more casting sessions, and instill more confidence in filmmakers the moment you enter the casting room.
So if you're an actor and you haven't yet built up your reel, then start submitting to projects that provide a mixture of comedic and dramatic content with the specific intention of using the footage from these productions as content for you future demo reels.
And filmmakers, if you've only shot one kind of story- perhaps it's important to branch out of your comfort zone, so that you too can broaden your range as a visual artist. For more information on demo reels be sure to visit the demo reel channel on vimeo: https://vimeo.com/channels/demoreels