Well, the setting description says:
"Benefit of improving action affinity by 1."
Internally, it is used together with the calculated benefit of increasing locality based on the communication rates / weights etc. I guess you could say it is "secret sauce" but it's also just very complicated and due to how it works, "tips" the scale from beneficial to detrimental with very little delta, so basically you might as well set it to 0 or 200. The internal algorithm is something we constantly work on and improve, the option to control it is just not very good (and should be a boolean instead of an int).
