I admit it's become one of those aesthetic mysteries to me. Usually they're just grassy setbacks. People might plant a few different things - a tree here, a row of plants or shrubs by the house - but they're usually mostly blank spaces. And they're blank spaces that nobody uses. Nobody (obviously "nobody" is an exaggeration, but basically true) throws a party in their front lawn, or even sits out there. Maybe kids play a bit on the front lawns, but not so much. Most of that activity happens in the backyard, the more hidden space.
People seem to love their lawns - and who am I to question that preference - but I don't really understand what they're for.