First of all, there is nothing as sad as trying to watch a wedding video that was shot by a family member or friend and all you see is the ceiling and ground and the backs of people's heads.
But the main reason you want it done right from the get-go is, once you have let a well-meaning friend or family member without the equipment and experience do this event for you, you won't be able to find anyone to FIX the problems that will be encountered.
Filming it right the first time is so important because fixing a bad video is next to impossible.