You would have not to worry about paying a lot of money if your computer goes wrong. For a G5 desktop, the AppleCare cost around 270 dollars for 3 years. If your warranty is already expired, then you would end up a hundred to a thousand dollar for a repair service.
A month ago, a tree branch fell and knocked the power line. Somehow the electricity killed my computer's logic board. It was my fault that I did not buy a battery backup device (UPS). It could cost me approximately $1,000 for the logic board replacement without the AppleCare. Now, I have a UPS. The AppleCare service is very good, and it gives me a peace of mind.
(The UPS that you could buy from APC or Belkin. They are good ones.)
