'Stretching' milk is the proper term for 'steaming' milk as in cappuccino.
The difference is that simply heating milk by means of steam results in froth whereas stretched milk is micro textured and has a sliky texture resembling wet paint.
This is what helps coat that tongue thus adding to the perception of sweetness.
It can only be achieved by heating the milk to the correct temperature within the correct amount of time which demands the correct technique.
This is what is on display when you see latte art like a fern or a heart or a tulip cast into a cup of coffee.
It is not nonsensical fluff.
The latte art is an indicator that the correct level of skill has been exercised in the preparation of your drink.
Oh right. I know what you mean now. Actually it's a common misconception that heating the milk breaks down the lactose. It requires water and an acid to do so, but they're in such small quantities that the result from increasing the reaction with heat is pretty negligible. That's why heating milk doesn't make it more digestible for those with lactose intolerance. They still suffer.
The misconception stems from people who felt fine after doing so, but as it turns our these people have an allergy to milk proteins - they're not lactose intolerant...