Without a backup at hand, any attempt at "serious" repairs could cause more issues.
Also, just like PCs, Macs have mechanical parts, and also software can become troublesome. I own a Toyota Camry (second one I have had), and if there is ever a dependable vehicle, that one is at the top. But, I STILL do some maintenance on it myself (like checking tire pressure, changing the Cabin Air and Air Filters myself, checking on the battery, etc.). And of course, I take it in for scheduled maintenance. The same applies to Mac computers. They are not invulnerable to issues. Yes, the occurrence of viruses is much less than on PCs, but there are still some out there that appear from time to time, and thus one still needs to exercise caution.