When I’m troubleshooting a computer I want to rule out hardware failures before I work on the operating system and software or malware problems. I like to test the RAM and hard drive for defects and if a computer has built-in testing diagnostics, it makes my job easier.
I was asked by a commercial computer client to wipe and reload the operating system on one of their desktop computers recently. The computer was slow and exhibited signs of malware. It would be stupid to work on this older computer without testing the hard drive for physical damage and luckily the computer’s startup menu had Diagnostics on the menu. The diagnostics ran and the CPU, hard drive and RAM were tested and passed. Now I could get on with the task at hand: getting the computer back to factory specs.