Here’s a great PSA by Glove and Boots about the pitfalls of shooting videos vertically. They make a great point and as a video editor I have received videos even for a news show shot vertically.
Before some of you get upset about whether this needs to be applied to all videos shot w/ a smart phone, yes there are specialized circumstances, like a store display that is oriented that way. But for most of your home videos, which a lot of vertical video is, if you plan on watching that video on a bigger screen than your cell phone in the future, it may not be such a good idea to have a lot of video in that orientation.
But check out the video and enjoy! Let us know in the comments if you do shoot vertical video, does this change anything for you?