Film is one of the very few billion-dollar businesses where the majority of players ignore upstream marketing. You wouldn't try to raise $2m for a widget factory without identifying and quantifying the market for widgets, yet this is the equivalent of what many film producers still do.
Pre-Greenlight Marketing (PGM) is where the producer has all the power.
After you greenlight, your marketing options are severely limited (and often extremely expensive) but before you greenlight you can optimise the script, genre, tone, and talent package to appeal to a very clearly defined customer, and very clearly defined consumer.
By analysing the recent (and likely future) marketplace you set in motion a chain of events that most well-balanced producers agree will result in higher-paying distributors in more territories, allowing you to reach and entertain greater numbers of both niche and mainstream viewers.