Also when you destroy a ship hidden in a corner, you only get to exclude half of usual surrounding tiles (since ships can't connect). So long ships of lengths 4, and 3 are best to be placed on edges, because they're going to be hit sooner rather than later anyway, while small ships can try dodge late-game shots.

Edit: just realized a lot of commenters here played a version where the ships can touch. My reasoning above won't apply in such case.