A writer trying to sell his screenplay is often asked "Who's the target audience for this?" Now, it's easy to hear that question and fly into a rage over how horribly commercialized Hollywood is, with films not seen as art, but commodities designed to sell stale popcorn and salty pretzels. However, all the statement means is, "Who will see this? Who will want to see this? What viewer will this film reach?"
Check out the comments...you'll be surprised by some of the reasons given.
I tend to divide theatrical releases into two categories: movies and films. 'Movies' should be experienced at the local cinema, whereas 'films' can be enjoyed at the local Cineplex OR in the comfort of my own home. And speaking personally, I'll be swayed by films brought to us by certain writers, directors, and/or filmmakers...stars, not so much anymore (you burned me one too many times DeNiro!), and movies that demand being seen on the big, or a bigger at least, screen. Thus I've stood in line to watch Transformers or Wanted as opposed to The Reader or Revolutionary Road, even though I know darn well the latter two will be much better "films". And as for commercials and trailers, they've become more of a turnoff than a draw for me of late due to their tendency to expose pretty much the entire plot. A clever poster can actually be more seductive and enticing.
Anyway, having a sense of who will want to watch your film and why is really important to know when you're writing your screenplay. Duh. But it's a question a lot of screenwriters never seem to get around to answering until it's too late, especially up here in Canada.
What makes you see a movie?