On the note of filming a trailer, most independent films have a concept trailer shot first. Often the trailer is used before final casting decisions have been made. That trailer is used, along with budget and profit projections, to make presentations to potential investors. It's also used, sometimes, to attempt to lure big name actors the project couldn't normally afford to participate in the filming, simply because they like the film. Ever see a trailer, then watch the movie, and notice that lines in the two don't always line up, or there may be scenes from the trailer that never actually happen in the movie? Those shots are often taken from the pre-trailer that was shot before the script was finalized.
As for the film itself, I kept asking "what's that 2x4 doing on screen? Oh, that's his acting!"