Preventing Angiocath Clot

Hello, all! Nursing student here getting ready to graduate and start working on an acute medicine floor in June. I have an angiocath question that I have to get cleared up. If you have a bag of fluids running and the bag runs out, does that create a risk that the angiocath will clot off? I had an instructor tell me that once and she was always on us to be sure to watch the clock and not let a bag run all the way out. We were either to disconnect it before the bag was finished (if there were no more fluids ordered) or else change out the bag before it was empty. But in clinicals, I see it happen all the time. So what's the scoop? Do I need to be worried about this or not?