Use it cut watermellons, or imortals trying to take your head (as in the series or movie "The Highlander"). But seriously, could that 20-inch knife be a machetti? It might be very useful for clearing brush and unwanted sapplings, depending on its heft. It will still probably be good for cutting large mellons that are too big for your 10-inch knife.
Seeeeeya; Goodweed of the North