So, I love these. I automatically think I’m cool just for finding a site with one. However! As with most things I find cool, you should approach with caution (I am also an enormous fan of puns, for example).
You have to keep in mind that too long of a video can affect load times of your site negatively, while too short could end up looking choppy and confusing visitors.
And speaking of which, there is some evidence that video is best used when you want to evoke a certain mood in your visitors; if the goal is a conversion (be it sales, leads, or just persuading/educating) you don’t want to distract your visitors from the task at hand (registering to vote, signing up for your newsletter, ordering a pair of shoes).
Divi lets you add background video easily (and put a translucent layer over it to camouflage low resolution videos, and there are of course plenty of plugins. Background videos are not loaded by default in mobile devices, but I believe Slider Revolution works around that nicely with Content Layers. Tell me what you like or dislike about background video – do you think it will continue to gain popularity?