Every accepted review is paid from a game's budget. When a game has paid for every review it can, it leaves the board and the next game in line takes its place. So a careful review pays you and makes room for someone else's game. The developer whose game just left comes back to review, earns tokens, and puts theirs back up.
That loop only turns if people give as well as take. Holding tokens and never reviewing doesn't help the site, and it doesn't help you: the board slows down and there's less for anyone to claim, yourself included.
Tokens hold their value for as long as the reviews here are worth reading. Developers want them because the feedback is good, reviewers earn them because the feedback is good, and the same tokens change hands again and again, in playtests and on the market. A Reddit thread can't promise you'll get anything back for your time. Here, the reward is held in escrow before you start playing.