From playing a few games of Random micro control, I've determined that the duration of ping in a smoothly running game is the exact amount of time that it takes between when you hear a ghost cast lockdown, and when it hits a goliath about 4 range away, and then for the medic to restore the goliath.
It's fairly small but still there.
The ping hurts players in millions of ways: it makes mutalisks and vultures much harder to micro.
And I considered how the split second time that people normally use to dodge storms could also be taken away. What are some good tactics that take advantage of lag? I know duration spells like psi storm get a huge benefit as no one can micro their hydras to survive multiple storms under lag. What else?