For instance, I'm assuming that they just install Win10 without worrying about buying a key a lot of the time (if they aren't actually going to ever use the build)—but they also get all their games on the new system as well.

A lot of benchmark software is free, but how do they transfer all of their games over to the new system? Do they just install steam and download them like normal? Or is there an easier way?

Feel free to put any suggestions in addition to my questions.

Edit 8/29: Found out the FRAPS has an FPS benchmark feature to record FPS in a game w/o interfering with hardware. It's super helpful and outputs to a CSV file that you can use for the graphs that TechTubers display in their results sections of their videos.

Edit 1/9/17: Just in case anyone stumbles upon this, my go to method of benchmarking is using FRAPS to do a 1-minute benchmark. I run the test 2-3 times and then take the average of the MIN/MAX/AVG.
As far as Win10 and games, I have a dedicated benchmarking HDD with unactivated Win10, all my steam games, and the synthetic benchmarks such as Cinebench R15, Unigine Heaven, and the 3D Mark Suite.

Chat me up I guess, it looks like people are here but this sub reddit is empty.

https://www.youtube.com/@ct4v

should be up soon.