Don't shut this out if you're a computer expert yourself. There's bound to be some area of expertise you don't have a handle on -- maybe home improvement or cars or understanding a very narrow genre of corny jokes. I'm sure someone would be willing to arrange a trade.
The Friend Who Can Watch Your Kids or Pets
If you have kids, or pets, you might someday want to go to one of the thousands of places pets aren't allowed, or one of the millions of places it's inconvenient to bring kids. Since leaving them alone means you'll probably return to a destroyed house where everyone's been electrocuted by chewed wiring, somebody needs to watch the little monsters.
Or maybe they'll invite all their friends over for a cocaine party or whatever the kids are doing these days.
Just like fictional detectives, you often have trouble finding someone with both motive and opportunity. It's not that hard to find someone to come by and feed your cats -- but caring for a dog starts to become a serious chore, and taking care of kids is a full-time thing. Even if someone is willing, they've got to have enough experience to handle emergencies, and the kid or animal has to like them enough not to shit on their carpet or bite them. There is only one other person that's able to enter my house without my black cat spazzing out and running for cover as if the house is being raided by Nazis.
If you're lucky, parents or relatives can step in, if they live near you, and if they're not terrible people you're afraid to leave your kids with. This is the opportunity problem, where the people most willing to do it live far away from you or work full-time (or possibly are in jail).
"So, uh, do you think you'd be able to watch my dog for a week?"