Back in the old days of 286s...
...I purchased a PC clone from some company that sold them for cheap. The PC ran fine till one day (I really wish I could remember the circumstances, but that memory has degraded), I needed to get into the BIOS setup. And the darn thing was password protected. From me. On my own PC.
I was furious and called up the PC guys. Their explanation was that some people get in and change options (specifically overclocking) and screw up their PCs. Thus requiring warranty hours.