Why video is important
It's not just on Facebook that video is important. Youtube was never more popular. Facebook is promoting videos heavily. It's a good opportunity to present yourself and keep the user on the platform. Of course, Facebook wants its users to spend as much time there as possible. Let's not get into whether this is good or bad ;)
Facebook doesn't like Youtube videos, for instance. These posts are gonna rank lower and not be shown as often as, for instance, videos native to Facebook. Facebook is not Google. Google doesn't care where we go after we search, as they are making money off the paid ads (AdWords).
Facebook favors not just the video posts, but also the video ads. Video is a good way to present a business, or an event using an ad. Whether the video is 30s or a minute, it's important that it's captivating, recorded in good light and good sound. The restrictions that apply to image ads (roughly no more than 20% text is allowed) also apply to video.