Find new capabilities on those sites (new spectrum, equipment, sector splits, etc.)
Know more about the network you're using
Diagnose problems. Even if you can't personally do anything about them, there's something satisfying about understanding why you're having a problem (and possibly how to mitigate it).
The green pins have been manually positioned by a user. The red pins are a calculated approximate (which can be way off). Sites can (and usually do) have multiple pins, for reasons.
It's way, way easier to collect the data now that CellMapper exists. It almost makes it less fun.