There's a common saying "we'll fix it in post," there's a problem with this attitude. Though many things can be fixed in post production (especially in sound), not everything in video can easily be fixed without reshooting the scene. Decisions made at the start of filming can save time later on. Such as shooting in the right perspective or choosing the right lens. 

Another misconception is that the lenses can solve perspective problems. The lens may make someone look bigger or smaller in the overall picture, but what is capture is still a certain distance away from the viewer and that will always be seen. 

The video below disproves this myth with a bunch of different examples in addition to detailed explanations: