Currently, if you select a file in the file explorer, the shift+alt+f shortcut does nothing, since you haven't selected a folder.
This makes the shortcut rather useless, since you're forced to select the folder first, in which case you might as well right click it and select Find in folder...
By allowing us to set a default, or just implementing "Find in root" as a default when a folder is not selected, the shortcut would have much more value.