I used to display Google ad links on my site, they accumulated value - slowly, but Google would only cut a check when you reach $100 worth of ads shown. My earnings approached $100 like an asymptote, halfway there in the first 6 months, 3/4 in the first year, 7/8 in the second year, 15/16 in the third… never did quite reach $100, and so my payout for all my effort and showing of their ads remains to this day $0.