re; about:config tweaks

[uripyores]

I suggested to a friend of mine to use this tweak that degsy posted and another person butted in and said;

some sites have found ways of either disabling the changes you make on your end if they increase site load or actually just denying service if it finds it"

He said that it puts too much strain on the sites and that it's "bad manners".
I disagreed with him but what are the facts?