Just watch the credits of any even moderately funded film and you will be reminded of how many specialists are required to make a movie. Depending upon the type of film there could be as many as a dozen department heads plus a dozen other specialists for production and another half dozen of each for post.
If you watch lots of "Making Of" DVD extras, watch films while listening to the audio commentaries and watch docs like "The Cutting Edge" you'll find that by the time the film reached post many directors are glad to let someone else wade through all footage and piece the film together. And if you go through a directors filmography you'll find that s/he will work with many of the same people on a consistent basis.
As the director your job is to, well, give direction. It starts with preproduction where you let the DP, and key dept. heads - grip, hair/make-up, production designer, wardrobe designer, etc. - know exactly how you want the film to look. You discuss with the composer and sound designer the aural mood you desire and with the editor discuss in depth how you want the story to evolve, pacing and the like. The key to making a good, solid film is the directors ability to communicate clearly and concisely what s/he wants to see and hear, listen to all of the suggestions that could improve the project and then leave the dept. heads free to do their jobs while the director works with the actors when shooting begins.
Filmmaking is a highly contradictory process; it is highly collaborative while at the same time the director is absolute dicatator - subject to the whims and quirks of the producers.
