Very rarely.
I repair medical equipment for a living. But I'm intimately familiar with many of the circuits. The others I have access to tech support and info not available end users. In other words, when I get in over my head, I cam get mote info than the people who operate the equipment. As such, nurses should not be repairing medical equipment.
The same goes for bass players who aren't electronics techs....and sometimes even those who are.
I have swapped tubes (with matched sets), swapped fuses, replaced two-wire power cables, and other basic stuff like that.
I was happy to send my Mesa Walkabout back to Mesa for servicing. Again, those guys know those circuits, and have bins of parts in the shop that I don't have access to. There is a lot of piece of mind that comes from knowing that factory techs went through the whole amp and sent it back ready to go another several hundred gigs.