It used to be that anyone who worked on airplanes knew how to time a magneto, clean an aviation spark plug, and safety-wire an oil filter. In fact, they could do those things in their sleep. They were the basic rituals of aviation - along with applying a fabric patch and tightening flying wires. But times change.
Today, we are likely to spend as much time with our computers as we are with the greasy stuff under the cowl. In addition to keeping our aviation databases up to date, we need to download and install new terrain and obstacle maps. And don't forget to check for software updates to your EFIS displays. And the transponder. And the GPS, and the Comm radios. Oh... and the autopilot! With that many updates to do, an external power supply isn't just a luxury, it's a necessity - if you care about your battery, that is. And woe to the owner/pilot/mechanic who lets the battery die in the middle of a software update.
Fortunately, once you have some power applied, the actual process is something that you can do mostly in comfort, sitting there in your cockpit with a cool beverage and some good reading to keep you company. The computers only need you to be there to start and stop the processes - they are more than happy to carry on by themselves, only asking your permission now and again to begin the next step. Nary a wrench, screwdriver, or can of dope is required. And if you have problems, you can get the fourteen-year-old from next door to help out.
Or to do it for you.