Basically, it gives few secs advanced warning, sufficient to avoid lift or come out of car.
I was in a 7.5 in Mexico City many years ago. It felt like a fast moving New York subway train. Coming home from a party my date and I ran to the middle of the intersection away from buildings and electric lines and were holding on to each other to keep from falling down for over a minute. Over the next few weeks I would feel an occasional shudder while I was lying down.
I was not real close to the 5.8 near Mineral, Virginia a few years ago, but my wall was shuddering intensely for about 15 seconds. I also needed some repointing done on a chimney. I kept a cup of water next to my computer and on 3 occasions I saw the water surface ripple. On two of those occasions I thought I felt something and a 2 or 3 aftershock was reported. The third was barely perceptible on the water surface and nothing was reported.