My lead guy went through a hard patch last summer. Started fibbing to me about time and truck usage. I didn't fire him for his transgressions so he quit. That's when I put the GPS in his truck. Two weeks later he came back
Tracking makes the crew leader think about time, route and speed. When lunch breaks are tracked social pressure gets applied to the slow lunch eater. My guys usually take 30 minutes now because they'd rather get paid. I don't have to waste the leader's time making phone calls to find out where he is and I can check route to see if they've picked up materials. If the truck is ever stolen we can send the police to get it. We all see it as a useful tool.