Well, right now a Plus One is worth 2.4 cents. A few weeks ago it was at about 9 cents, but then the cryptos crashed. Several months ago someone on the Plus One board sold 4000 of his coins for about $250, so they are worth... something. Maybe one day they'll be worth more, and maybe not. But they ARE free. (You can, of course, buy them, but I don't think many IHubbers are interested in doing that.)
And you can also use them to award posts you like. Even your own.