If they don't slow you down normally then carts still have a good function, if you combine them with healers. After battle, especially when fighting monsters etc and you need to get around quickly, then it can be good to just travel using carts rather than waiting 1 or 2 turns for most of them to heal. It allows for a little bit of extra manouvrebility. Or let's say you had a big fight and want to chase down the enemy, could be worth it.
Maybe on Dwilight. On other islands, I don't think the travel hours is long enough for it to benefit much.
