It only matters if Erf is small enough that circumnavigating it is feasible. If it takes ten thousand turns by dwagon to go around it, it might as well be infinite.

If it was finite, that would matter to the sides on the edge, but probably not to the sides far away from the edge. Right now, it really doesn't matter to anybody in GK whether erfworld is infinite, or whether it's finite but you can loop around it if you travel for a long time, or whether it's finite but the edge is really far away.