Why would dogs hang their tongue OUT?

Most of time we have heard that people certainly map one's nose to dog's, when he or she could typically figure out something by smell. But the thing caught my attention while looking at the dog why dogs would have their TONGUE hanging out! lol
It's known for smelling sense... But tongue out for? And not every dog put it out just when it is hungry, although few does it but more randomly.

Any guess why it does? okay have you ever noticed a dog sweating either when it is tired chasing or in the street even sunny day. I hope by now you might have recalled any situation if you have lately seen any dog hanging their tongue out post reaching you by run.

Strange part here is that, they don't have no sweat glands except for on their tongues so they poke their tongue out to cool off. Dogs have a high body temperature and they hang their tongues out to let heat out through their tongues. So it's just their way of relaxing; rather than pointing it as sweating.