I think the trick is to sort of have an idea where you're going with your plot, but to be ready to leave the trail and scout out the off-trails. And sometimes, just writing, just walking, just doing, leads to possibilities unimagined. While it can be good to have trail markers and a map, (the outline) - it can be a real adventure to just go and see where that road leads. Unfortunately, sometimes you just get lost, tired, and frustrated.
Still, that piece of wasted writing, without plot, does let one develop some endurance, some writing practice, and some understanding. A trail - a plot - can't be far off.
Now hasn't this been a real meandering, plotless post?