We have a few deleted trucks in our fleet. Reliability goes WAY up (from once a week with expensive repairs breakdown, to none). Fuel Mileage goes up. Engines run quieter, cooler, and have more power.
Downside? What downside, unless you are still under warranty, or live in one of the ****** states.
But if Commiefornia gets there way, in a couple years, a deleted truck wont be able to even get plates. Tuners are already working on a get around for that one too...
Right-To-Repair, depending on its outcome, will have a big impact there.