If you want to be safe from random edge cases (like someone in front of you slamming on the brakes), slow down.
But Parent suggested that it's a good idea to leave more space in case someone jumps in. I'm not sure I understand that - if they jump in it's always dangerous because you don't know what the person behind you is going to do and you don't know when the jumper is going to jump in. Thus, you want to try to prevent them jumping. This is achieved not by giving them more room (which encourages jumping) but by leaving less gap (reducing jumping) but still leaving the safe minimum.
Do I actually leave that much space in front of me every time I drive 70mph? Hell no. But the slower the cars beside me are going, the quicker i'm going to hit one if it pulls in front of me. If they were going 70mph too, I would only have to brake down to, say, 65mph, which would should only take a second. But if they're going 10mph, I now have to come to an almost complete stop to prevent from hitting them, which as you can see above is a lot of car lengths.
If someone in the lane beside you might cut in front of you, leave more space so that you can see them making their move and react in time. That reaction might be to speed up and prevent them before they change lanes, or to slow down and let them in, but in either case, leaving more space is a better idea than tailgating.
A lower speed increases the chances of this, but reduces the risk of a catastrophic result. ;)
