As Scrooge mc soupy says, it's not a trust issue.
The benefits are you can see instantly how the day is going, you get cheaper insurance, we can now prove, if needed that we were on site (when and how long)
For us it quickly highlighted some problems which some jobs time wise, which we can now address.
Also, like everything if your too familiar things start to slip, 5 mins here, 10 mins there, before you know it your paying extra hours all over the place and it can be hard to address this without knowing where things are going wrong, the guys have to meet an average hourly production rate to get a bonus, the tracking has helped with this and we work far more efficiently than before
Darran