They add a subtle flavor when used as aromatics in broths or stocks. I actually have some as of now waiting for that exact use.
Otherwise, you can use them as a starchy vegetable, though not as starchy as potatoes. Try steaming and mashing with some butter, or chopping with some other robust veggies and doing a roast.
Yesterday, I put one through the julienne setting on my mandolin and pan fried it until it was flexible: fast noodle replacement.