Many times one of the Search constraints in “Do a Search for…” involves a field on an object that is a list and the comparison is with another list in the UI. For example, my User Object has a field called “Favorite Restaurants” and it is a list of Restaurants. If I wanted to Search to find a list of Users whose Favorite Restaurants matched the Current User’s Favorite Restaurants, I’d need to get All Users and then use an “Advanced…” filter. This can take a long time as the App gets long and the lists get long, too. If I could find an intersection of these lists in the DB, that would be faster (especially if I only need a count, I shouldn’t have to load any Users to the browser).
Please upvote this feature on the idea board here: