The app icons work just like in the dock; you either open the app from there or more likely, you select a bunch of files in the folder you’re in and drag them onto the app icon to open them. That’s faster than dragging down to the dock or right-clicking and choosing from a list of options.
So, dragging a bunch of icons UP to the app in the toolbar is faster than dragging the same icons DOWN to the app in the dock? Good to know.