the latte is a newer drink. I is SUPPOSE to be layered so that the froth cuts the cema and espresso to ~ capp strength and the mostly pure milk at the bottom cuts the acid of the coffee and kills coffee breath. Nobody does layers anymore. Kinda sad. looks real like a freshly poured Guiness if you do it right.
Most important, however, is texture. Properly foamed (see: Microfoam) milk has a creamy texture thanks to trapping all those fat globules in the whey protein matrix. That's what cream is mostly used for in culinary arts... texture.. the velvet feel in the mouth. Good foam is heaven sent being a perfect balance between solidity and fludity, between it's persistence and evanescence. Substantial, yet smooth and seemless.
Also: it both keeps the drink warm longer AND shields your tastebuds from that harsh heat. It makes hot lattes (those bastids who steam over 150-160 range just WANT to be hurt) drinkable. Also: without it how are you going to make that pretty bunny on top, or the coveted Rosetta.
No... foam seems to be going out of style with modern amercian tastes. "It just wastes space in my cup. I want more coffee." When they're not getting more coffe they are just getting more milk. I'm abhord by this behavior and you should join the fight to stop these people. Educate them that foam MUST be atop a lattee because without it it's just a nasty drink with hot milk.