Some companies do great on mobile while others perform quite poorly. If you have significantly worse mobile than desktop data, we'll how an alert on your dashboard. Just click on the alert to go to the campaign screen.
You'll be instantly taken to the view where only campaigns with underperforming mobile traffic will be filtered out. Click on the red warning label in the Device Performance column to view more details so you can understand the difference in metrics.
In the detailed view, you can make bid adjustments or disable mobile devices from showing your ads.