We've all known movies are not shot linearly. That the ending might be shot before the beginning and after the middle.
We've also heard a lot of desi actors praising the likes of Mani Ratnam and a handful of others directors who provide them with a script before the shooting starts. I used to wonder why the other directors would not give a script, and how on earth you could make a movie without a script.
Think about it. The key problem in the optimization of movie making is probably not actor management or shot management, it's location management! It probably takes anywhere from 1-3hours to setup or tear-down* at a location. This shot might last a minute or two. Perhaps even five. If the unit tried to make a movie linearly according to the script, they'd end up with at least 4 hours of setup/teardown for each shot. Given a three hour movie with perhaps 50 (optimistically) changes in location, you'd get two hundred hours of setup and teardown alone! Not very pleasant!
Consider the alternative that innovative editing brought. You shoot all your shots at a particular location at one go, making sure that continuity is preserved carefully. Finally since this is film** and you can cut and splice, when all the movie has been made, edit the movie into its final form.
What does this do to the location management? Perhaps you have only 10 different locations, voila, setup and tear-down now occupies only forty hours!
What does this editing do to the actors? Since different shots are expected to be at different times, morning, evening and night, optimally, you'll need to schedule the shots according to the time they're supposed to be and not linearly per location either. So the director and assistants have the unenviable task of ensuring continuity in the look and clothes and expressions of the actors. The actors who typically have shots of between 60-180s, do many of them repeatedly and in a completely (in their reference) bizarre order.
If you're still having trouble, imagine a typical Tamil romance, with shots in the hero's and heroine's houses, their college, and perhaps a bus. All the shots in the bus might be filmed first, with the hero having little clue of how he's supposed to react to the heroine initially. The shots in the college may be filmed last, when they are most comfortable working together, but may in fact end up at the beginning of the movie, when they're not supposed to be! Little wonder that many actors end up looking lost in their roles! They don't know how they're supposed to act!
Only the director knows what he's trying to achieve. Between these hundreds of shots, each with different characters and different takes, is it any surprise that many directors take the easy way out and meld the script to suit the good shots? Thus the surprise that actors exhibit when they realize the movie they thought they were shooting, was, in actual reality, quite different in the mind of the maker. Add in last-minute or rolling suggestions from the producer and other influential (read financially munificient) people and the movie may end up being very different from what it was when it began.
This is forcefully brought out in a seemingly prosaic comment from Kamal Hassan***, who was asked by a reporter whether he was expecting a movie to be a hit when he was making it. Paraphrased from memory, it goes, "We expect every movie to be a hit - otherwise we would not be making it. We expend every bit of energy to do that in every shot. But at the end, when we see the whole movie, we see that this part could have been better, or that part different. By then it's in the hands of the public."
Hence the praise for good directors who provide scripts up front. Hence the generous praise for editors who do a good job, mostly from industry-insiders who realize the work involved, from a huge pile of mostly useless film.
So the next time you see a movie, count the number of shots, and the number of changes in locations, and the number of locations. Then estimate the amount of time it would have taken, and appreciate the skill of the editor!
* This ignores the setup and tear down involved in a particular location, which will still play a very significant role. Also permissions and dates are needed for shooting in public locations making things even more difficult.
** The advent of digital cinema may make for easier editing, but site setup/teardown is still going to be as involved.
*** Yes I'm a Kamal fan(atic).