I am also new but my theory is to leave room if it's hot drinks (I think some people like to add there own creamer or additions) and I just add more ice if it's cold drink. or maybe they just found a loophole lol.

I use extra ice. Lots of people do this thinking they’ll get a free larger size but in reality it’s just extra ice 🤷🏻‍♀️

ur supposed to leave room unless they specify that they want extra whip, extra foam, etc. the worst is when they order a tall drink in a venti for example, and then complain its not filled all the way. like what did u think was gonna happen?

People might want extra ice, extra whip, room to add something to their drink at home or work, or room to avoid spilling the drink in the car. I’ll usually ask, or just leave room if they don’t specify anything.