I'll add to the advice - if you need them, from too much sag they will help. Both in ride and handling.
The rear springs are progressive, the further you push them down the rougher the ride. A lot of rear sag also changes the steering angles on caster. That won't wear your tires but will cause it to road wonder.
If you need them they are great, if not then it's just something else to keep working.
I have the Firestone Ride-Rite 2540 Wireless Air Command Generation II.