I think it depends on the cat and your comfort level. I can't leave my cats alone for any longer than a day. Because of me and them.
Its what we all prefer. I can't help but think about if something were to happen to the house or the cat got sick and no one knew....I can't stand to think about it.
Also, if your cat is used to being social and having people around it can be difficult for them to all of a sudden be left for a long period of time with no interaction. It looks like you just have the one also so it will have no other living thing around for 3 days. Seems like a long time to me.
You can ask around at vets offices if you have no one you can count on to check on your cat. Sometimes techs will cat sit as a sideline. You can also look online or in the yellow pages.