If you never clean the drain line for your air conditioner, then you are probably going to come to a time when your air conditioner will freeze up.
A backed up drain line can cause a lot of problems. Green algae can begin to form inside the drain line if the line is never cleaned. When I was living in my first apartment, I had a huge leak. I came home from work and took off my shoes by the front door. I started walking over to the kitchen and I felt my foot get wet in the hall. All of the carpet in the hallway was completely soaked with water. I called the apartment maintenance staff and told them about the wet carpet. They told me that the AC was probably leaking and they would call the repair company. The AC repair company was there in less than an hour and they cut away the carpet and the padding so they could dry the area. They also used a machine to suck out all of the dirt, debris, and algae from the drain line. They told me to wait an hour before I turn the AC unit back to cooling. The sound of the blower that dried the carpet was horrendous and I was awake all night long. Thankfully, the carpet and carpet padding was dry in a few days. After that problem, I tried to find apartments that did not have any carpeted areas. Even though the area dried quickly, the smell of old, musty water never left the apartment.