I see a lot of people around my neighborhood putting what appears to
be some sort of soil or compost on the problem spots on their lawn.
What are they putting on their lawn and what is the purpose of this?
Is this some sort of lawn care cure-all or are there specific
situations in which this is a good thing to do?

By the way, I have a St. Augustine lawn, as do most people in my
neighborhood.

Thanks,
Dave