We spend the summer waiting for the inside of our vehicles to cool down so that we can commute in comfort to work, school, home, and more. Air-conditioning systems in today's cars are quite advanced from thirty or even twenty years ago. Vehicles now will hold less refrigerant and because of that, they will exhibit less cooling in the car if the system loses a small amount.
The big issue with refrigerant loss is that the oil in the system is also leaking out, which can cause extensive damage and costly repairs. The oil is designed to travel with the refrigerant and lubricate the compressor. When the oil level gets to be too low, you can sometimes hear the compressor making noise. This is not a good sign.
While the compressor is starving for lubrication, it will start to wear and cause particles of metal and other debris to work their way through the system. In order for the cooling process to work correctly, the system needs to be free of any debris.
Eventually the compressor will wear enough to quit doing its job and the debris could restrict the cooling condenser and need replacing. Each situation is different, but condenser replacements are becoming more common.
There are products available that are being used to attempt to seal the system by simply installing this agent into the system. I personally do not recommend them and will not work on a system that has had such a product installed. These products cause extensive damage to expensive machines used to recover and recycle the refrigerant from vehicles.
If you have not needed any air-conditioning work done in the last couple of years and just want the performance tested, then I recommend adding a small amount of the correct oil to your system. Some oils will have a dye mixed in, which makes future leaks easier to locate.