Similar to writing, being concise in a video is key. You don't want your video to take any longer than it absolutely has to. You'll want to remove any extraneous material through editing. And just like writing, editing video takes time. Depending on the complexity of the material, one minute of finished video can take hours of editing. Hours of editing may not be necessary for a quick demo or screen movie, but it's worth keeping in mind the time involved in editing media.