FreeRice.com donates 20 grains of rice to the UN World Food Program for every correct answer. The pessimists will immediately say, "What goos is 20 grains of rice?"
For one thing, if you love proving your vocabulary is good, you won't just stop with one correct answer. And, if you don't have anything to do, is whiling away your time, escaping your work, bored, etc., it's a good site to spend time on.
Another is this: If one million people got a correct answer, then that's already twenty million grains of rice! Surely that's at least enough for a decent meal? And if a million people got twenty correct answers, then surely they've just provided a family of four about five meals. Isn't that the greatest thing when you're only just polishing your vocabulary?