How high is high? I usually raise ours up to maybe 3 - 5" (have never really looked that closely). It may depend partly on what your jack rating is too. If a jack had a 3,000 lb rating and your tongue weight was say 800 lbs, you'd be able to lift up to 2,200 lbs of the dead/static weight of the truck. The higher you raise the truck, the more force is required since you are relieving weight off the truck's suspension. If you have a manual jack, you won't want to raise it more than you have to and you want to raise it just enough to comfortably get the bars on and off. The amount you have to raise it will change depending on how you are parked and what the angle of the truck is relative to the trailer. With a 1/2 ton truck this should be fairly easy to do. If you have a heavier 3/4 ton truck with stiffer suspension, it's somewhat harder to wind up.
I doubt you are going to damage anything unless you have significantly overloaded your truck by towing a trailer with too high a tongue weight plus too much load in the truck bed and then I think the jack could be damaged, but I've never heard about that actually happening.
If you don't have an electric tongue jack, they sure help!
Gil & Deb & Dougal the Springer Spaniel
2014 KZ Spree 262RKS & Ford F250 supercab V10 4x4 LB