Whenever I play songs/melodies where I have to pick along multiple strings, I have been only moving the angle of my wrist while keeping my elbow at the same spot when moving to another string, but I recently saw a video where it was instructing to push your elbow in when going down the strings and then pull it up when going up the strings, while keeping wrist movement minimal. I've tried to search online to see if this is a good idea and should spend time focusing on it or if it doesn't really matter. If it makes a difference I mainly play acoustic guitar. Should this be something I put a lot of effort into learning or something completely unnecessary? 

If it is something I should learn does this also apply to strumming or mainly just picking?