If I lay up to 100 rather than 50 it's because I'm not feeling confident with whatever club I need to hit to get to 50. If it's a par 5, I probably feel more comfortable hitting 6 iron than 3 iron or 3 wood. But all things being equal, closer is better.
Plus, half-shots can be cheated quite easily if you're not playing well otherwise. I can have a bad case of the lefts with my full swing, but on a half-wedge, I can more easily swing dead-hands, or I can put the ball back in my stance, or several other things. But if I'm swinging really badly, there is not much I can do to fix it.