Why is spawning a new process per benchmark more accurate?

[sleighsoft]

I stumpled upon an explanation of the differences between timeit and pyperf here: https://pyperf.readthedocs.io/en/latest/cli.html#timeit-versus-pyperf-timeit

I am wondering why spawning a new process to benchmark is better?

Edit: I assume this has something to do with it? https://vstinner.github.io/journey-to-stable-benchmark-average.html