It's the weapon that Unseen Power dreads most, and if he can get us to treat it as casually as we treat a pair of skis or a tennis racquet he can keep his hold. That question assumes that results ought to be measurable. His thoughts are as much higher than our thoughts as the heavens are higher than the earth. And he is Love. Infinite Love will never give a stone when bread is asked for, or a scorpion in place of an egg.
Prayer is compared in the Bible to incense.
Incense was very expensive, blended by a perfumer according to a strict formula. It appears to serve no particularly useful purpose. Its smoke and fragrance soon dissipate. Prayer is like incense. It costs a great deal.