Exchanging one clip with another
Multicam angles are a delightful luxury, but even without them, you've got more flexibility than you might think. If, for example, you prefer one reaction shot to another, it doesn't matter if that reaction was reacting to those exact words at that exact time — it can be from any take, as long as nobody's lips are seen moving incorrectly. If you can see someone's lips moving to words you can't hear, or see lips not moving when you can hear they should be, you're pretty much locked into the matching audio for that shot.
Important Note
Once you realize this, you'll see that reaction shots are frequently "cheated" in this way. An editor will often end up choosing the best reaction shot, and if you can see the head movements of a person actually speaking, you'll notice that the words they're saying probably aren't quite in sync, or worse, are from a completely different part of their...
