Are you judging dogs by the standards of human behavior? It would be completely useless for a human to piss all over the place, but for a dog with orders of magnitude better sense of smell than people, that urine odor will linger and be picked up by other dogs.
A dog’s sense of smell is so good that some studies have demonstrated they can reliably detect cancer in human urine.
A dog’s sense of smell is so good that some studies have demonstrated they can reliably detect cancer in human urine.