The refrigerant in the air conditioner contains a special oil that lubricates and cools the A/C parts.
When enough refrigerant leaks out, your air conditioner still makes cold air, but the parts don't have enough oil to protect them and they wear out faster than they should so it's important to service the air conditioner as recommended by your San Antonio TX service center.
Replacing old refrigerant has another benefit: refrigerant tends to gather moisture and become corrosive. That causes leaks in the system which can be expensive to repair. Fresh refrigerant protects the air conditioning components and keeps the system operating at peak efficiency so it doesn't have to work as hard to keep you cool.
Even with regular service A/C parts can just wear out. Normal wear and tear eventually gets to all moving parts. Addressing early problems can save on more extensive repairs down the road. For instance, a common failure is the clutch that turns the compressor on and off. If you can take care of a bad A/C clutch when it first starts having problems, you may be able to save the compressor. Wait too long and you'll have to replace both.