If you want to get a performance hit from your machine, reformat, and reinstall. Not sure about these days, but this is how I would do it if I was playing competitive quake:
Format HDD
Install O/S
Defrag
Install primary application (Quake)
Defrag
Play
About every year or so on gaming rig:
Format HDD
Defrag
Install primary application (Quake)
Defrag
Play
Cause it clears rubbish that builds up.
Leave the SSD to run the OS and the primary app, put all the other shit on a large drive. Back in the day we had a smaller HDD just for the OS and primary app for speed. The larger drive held the bulk. Now days, the SSD may as well run your OS and primary apps, and your bulk can still sit on the big old HDD.
ahhh when i was a lad...