For example, a stick or channel of system RAM may fail training at boot and end up being silently disabled. CPU-Z would blindly report all memory channels being present despite Windows task manager showing correctly that some of the memory are unavailable.
Just start task manager, ctrl+shift+esc...
(BTW to me owning a computer and not knowing what's inside is like not knowing what brand of car you own [never owned a car personally but I imagine this analogy works for most].)
So now I run the tools and save the info on my harddrive to be able to look up before I go home to someone to fix a computer.
It's more like not knowing what type of engine your car has.
Most people don't know or care what type of engine/cpu they have, they just know the brand (and maybe model) of the entire machine.
I'm a tech person and I don't even know what CPU is in my computer right now. I know I have a thinkpad x1. I know I paid for the i7 upgrade. I know where to find the CPU model if needed. But day-to-day I just don't care.