It's largely useful on mobile devices because you can easily forget them somewhere and all a tech savvy person has to do to get the data is remove the HDD (if it's a laptop), or if it's integrated, reset the admin password with something like NT Offline Password Reset. Smartphones are another can of worms I won't get into, but I'm sure you understand.

With a desktop, it's highly unlikely you're carrying it around and will forget it some place. The only way someone can get the drive is to break into your residence and physically remove the drive, and as someone else said: if someone is breaking into your residence to get a HDD out of your PC, you have bigger problems.