In my opinion, the leaves should be removed from the lawn. Not just the leaves, but the pine cones, pine straw, sticks, nuts...all debris. In my experience, this debris does 3 things: it is unsightly and you're neighbors are indeed wondering when you will be cleaning it up, it invites fungus and other diseases, and it can squelch out the grass in the spots where the hard debris lies.
I think, though, if you are talking about purely "leaves", that when properly chopped up into fine particals with a true mulching blade fall back into the turf and break down then, sure...mulching could be of benefit. But what this translates to for many people is running a loud, dust creating riding mower with a standard blade over anything and everything in the lawn...which supposedly saves time and is good for the soil.
ALSO - lol - playing in leaf piles, although quaint and picturesque, can lead to bringing wolf spiders, mites, ticks, lice, and who knows what other creatures into your home *cringe* :)
This is your yard boy Ash, over and out...