In simple terms, this means you can now tap on multiple screen elements at once. There are a ton of positive implications of this. First, if you hold your finger down on the screen, your hero will follow your finger wherever it goes. No more spamming the screen with a million taps (if you don’t want to)!
Multi-touch also makes it possible to use many abilities more easily. For example, when lining up someone’s global ability (like Kestrel or Celeste), you’ll be able to move the camera around with the mini-map and activate and then use an ability. You no longer have to execute a weird sequence of alternating touches to do certain things well, nor worry about losing a crucial tap to an accidental multi-touch.