Users are human beings and loves visual content. So, a promotional video briefly showing the key features of your app helps them down your sales funnel. Think about this as part of your user acquisition strategy. This is the big chance to get them to use your app, where the real magic will happen (and you will extract some hard earned $ through your clever freemium model).
In an increasingly competitive market place, App developers will need to add videos for apps or game trailers to increase their visibility and help users hit that "Buy Now" button. The good news is, we're making it affordable.
For Android, in Google Play is all about SEO, not just keyword stuffing in iTunes connect after spending hours on SensorTower.com. As Internet Marketers know well, creating a video with a link to your app, hosted on YouTube (owned by Google) is a strong SEO link which helps ranking.
This site helps you in all means of marketing that you need for your app.