OK I have a 25 year old house in suburban Chicago. Central AC is about 22 years old. I had it serviced Friday for the first time in a long time and I'm 2# short which the tech added (I wasn't home so thus my question). I knowthat fluids for everything need to be at the full level (oil, coolant car,for example) and I understand what happens if oil or coolant is low. What's the harm/ benefit to my system to have the correct amount of Freon? Will it run better, cooler, avoid future problems, what?