We live in a world or precision where data-generating technology is available for practically aspect of your life. We're also bombarded by tools to help us plan everything down to the smallest detail. But without uncertainty you're stuck in a place where you always think you know the answer, and this can be a major encumbrance when you're trying to get things done.
As Jonah Lehrer points out in the popular tech magazine Wired:
Vagueness is not without virtues. Sometimes, precision is dangerous, a closed door keeping us from imagining new possibilities. Vagueness is that door flung wide open, a reminder that we don't yet know the answer, that we might still get better, that we have yet to fail.
He gives the example of how an attempt to lose weight can go awry if you weigh yourself and are concretely aware of your progress. If you're making the progress you hoped for (or better), no harm done, but in the event you fall short of your goals the precise data makes it difficult to avoid accepting the fact that you're just not doing as well as you'd hoped you would.
If you don't know your exact progress, however, your confirmation bias (the phenomenon that essentially causes you to believe what you want to believe, evidence be damned) can actually help you to keep going. Just dieting and exercising can make you feel like you're making progress so much so that you'll have no trouble convincing yourself. If you step on that scale and find out you progress is slower than you thought, however, you may lose some of your stamina to keep going.
Of course, this doesn't mean data is something you should always ignore. Sometimes precise information can be useful (e.g. it helped me to sleep better). While it's good to know the facts in some situations, if it's hampering your progress you may find you're better off left in the dark.
In Praise of Vagueness [Wired]