Just did mine yesterday. More to put some more oil in the system as I have a jangle sometimes from the compressor and hoped it may help.
Very simple to do, but modern systems shouldn't need refilling as they don't leak like old ones.
Actually, modern systems do leak and when you think about it, it's obvious why. Your home refrigerator may run for 30 years because both the motor and compressor are sealed inside a metal "can". Your car's compressor; however, is belt driven from the engine and the compressor shaft has a seal separating the refrigerant from ambient air.
True, modern seals are better than in years past, but they're still conventional lip type seals and they do in fact leak a little bit. Therefore, over time, you can expect your air conditioning system to be low on refrigerant. It's good practice to run the A/C at least once a month even in the wintertime to keep the seal in good shape.
Some people never run the A/C and it's no surprise, (to me at least since I hold a license to handle refrigerants), that the systems won't work when they're ready to sell their car 5 or 10 years later.
Although a person might get away with simply dumping in a can of refrigerant, I would say you're MUCH better off if you at least attach a set of refrigeration gauges to the system while topping off. Of course, you have to know how to read the gauges.
It would be unusual to fix a problem by simply adding additional oil.
If the system was working and suddenly fails, then it's good practice to find and fix the leak first and then pump down the system, and refill with the proper amount of refrigerant.