In reply to tehmarks:
Well, imagine a situation. You have a nearly perfect conditions which do not last long, i.e. mountains covered in clouds, sun positioning, your own position if you are moving. You end up asking yourself such questions like:
* Will the loch look better this evening or next morning?
* Is it better to move uphill to take the shot of the valley?
* Are clouds going to move?
etc.
The usual answer is "I don't really know". Maybe professional photographers are more experienced at that as I shot about 40 films in my life (well, I am 21 and had a DSLR for half a decade). Even so, you can't make sure the next morning will not be misty, etc.
With film, you sometimes have to rely on luck or take several similar shots. With digital camera, you can just take photos as many times as you want. .