No, you don't have to. The routed subnets are there primarily to solve the problem for people who have CPE type devices like Fritz!Box and OpenWRT etc who before wold have to wait a week before requesting a subnet so they could actually use it. These are there per default thus everbody can enjoy them. By selecting the subnet icon on the webinterface and there enabling it. They are per default disabled for existing tunnels as otherwise a couple of the TIC clients enabled in CPEs that are out there get confused. For new tunnels they are enabled per default though. You can just keep on using the existing subnet. We rarely finally remove prefixes from accounts unless the PoP runs out of them, a that point in time we sweep them all up and clean them up. The "default routed subnets" are there per default and cannot be removed unless the tunnel itself is removed.