Remote hardware diagnosis
A friend's desktop would boot, then crash or blue-screen under load. A local shop wanted more than $150 just to diagnose it before doing any repair work. I did not have the machine in front of me. Everything was done through text messages, rough phone photos, and instructions written for someone who did not already know what details mattered.
The first problem was information quality. I had to work from partial views of the motherboard, PSU cables, RAM, cooler, and a spare donor system, then turn each next step into plain language. We started with memory, moved through individual modules, then cross-tested power delivery with an older PSU and the correct cables.
In about an hour and a half, I narrowed it down to three separate issues that were masking each other: unstable memory behavior, a power-related problem, and a CPU cooler mount or paste issue that changed depending on the physical orientation of the case.
That is the kind of troubleshooting I enjoy. The value was not one clever guess. It was isolating variables, keeping the user calm, and turning a vague "my computer keeps dying" problem into a clear repair path without making him pay just to find out where to start.