I've answered this before but I can't seem to find it now. If you you, that thread has more info on ancient amphorae.

Two basic theories: A) the pointy ends were meant to slot into the cavities created by arranging a base layer of amphorae in racks on a ship. Imagine a ship's hull, with no decks, lined with racks with holes. Then the next layer slots into the cavities formed between the pots of the base layer. Example

B) that the shape was simply to fit into premade racks on ships, for stability in heavy seas. Example.

The "pointy" amphorae were not used for anything except transport. When the contents were distributed, they went into smaller vessels for sale.