Imagine you get hacked, or you had to modify a plugin’s core.
Now, all these plugins (hacked or modified) need to be reinstalled.
You can not do it, you can not “fake update” them too.
You have to delete them, then reupload them, boring.
Now, just check each plugin’s box you want to be reinstalled, chose “Update” in the action select box, “Apply”, done!
WordPress will now let you update them even if they are already up to date 😉