Tagalys calculates the popular searches in each store and updates them based on historic search data. As a business your needs to promote may always not be based in historic data. Like a brand/category promotion etc., here you can pin this promotion at a position of your preference, and it will update the Popular searches viewed by your visitor, thereby influencing their visitor experience, making them that promoted search query is actually trending when it was pushed to the in that position by your marketing team.
A similar example at Target.com can be seen below
Pinned searches are a subtle way of push marketing, to influence visitor experience, conversion rates and revenues. Pinned searches along with Search Merchandising are a great way for your marketing team to influence visitor engagement.