things I use it for personally:
Early game was using it to cart copper/tin from the black forests nearby back to our base, as there is no weight limit to the cart itself and it has 4x2 inventory which is nothing to scoff at when hauling metal ore that weighs 10 a piece.

Mid/Late game I have one sitting by our dock on the opposite side of our island so when we come back with a literal boat load of iron/black metal/silver I can dock the boat and load it on the cart to transport the rest of the way to our base on the other side of the island

as to why we do it that way, it's much faster for us to do that than sail the boat around the entirety of our island