Remember, your audience has probably never seen your movie before. They may need help to interpret what they supposed to be seeing. So it's important to build up your shots, so that the viewer can relate each shot to the previous one and the shot that follows. The longer your piece, the more important this principle becomes, that's if you want the movie to "flow" as a story.
In turn, building such continuity requires that when you're on location, you shoot as much as possible with editing in mind.
On the other hand, it's difficult to ensure complete continuity when you shoot. Also, in some circumstances, you'll want a longer transition between shots or sequences of shots. Like a dissolve.