Most likely you would be wasting your money.
According to this article, 0.05 grams per kg of bodyweight is "sufficient to maximally stimulate muscle anabolism." That calculates to about 5g a day for someone my size (200 lbs). Now I understand this is just one article, but you also consume leucine in your normal diet, whey, etc, so it would seem to be overkill to directly supplement more than 5gs of it.
Now, I will admit I am being a bit hypocritical because I consume more than 5 grams of leucine via supplementation, but that's because of amount of BCAAs I take pre/intraworkout; I don't use pure leucine.
Yes, leucine has been shown to be important for muscle growth (in fact, likely the most important amino acid); however, that doesn't mean supplementing a whole protein shakes worth of pure leucine is going to have some incredible effect. As long as you hit that 5 grams consistently periworkout, that will have the most profound effect on your gains. Taking 4-5x that amount will have the most profound effect on your wallet, since you'll be having to buy 4-5x the amount of leucine.