Walking home tonight, I saw yet another driveway freshly painted with that black tarry “driveway sealer” goop. What does that stuff actually do?
I mean, it wears off after a year or so, and it would seem to be useless aganst cracks caused by shifting of the soft asphalt layer on its subsiding gravel base. So does driveway sealer combat some sort of UV-induced driveway degradation, or are we just talking about another suburban appearance fetish, like perfectly-uniform 2-cm grass, spherical trees, and Lincoln Navigators? 
While the sealer does need to be refreshed pretty regularly, an unsealed driveway will deteriorate much faster than a sealed one.
Technically, the sealer makes the asphalt more water resistant. It’s water, dribbling through the semi-porous macadam mixture that tends to settle the dirt or loosen the sand underlayer. (Same thing that causes potholes, for the most part.)
The less the underlayer moves around, the less the semi-flexible asphalt moves around.
But yes, some do indeed use it to get that “freshly painted” or “new asphalt” look to their driveway.