Prickly Ash may not be everyone’s cup of tea due to the rather large thorns. You may not want to casually plant this tree in a space where, say, you will be playing a game of tackle football. That said, really, Prickly Ash is remarkable and rather decorative. The compound leaves and clusters of red capsules also add to the look, providing a fair bit of visual diversity, as there is nothing that looks like Prickly Ash.
Hedgerow/Barrier: This would make an interesting and beautiful hedgerow. As a bonus, whoever, or whatever, tries to push its way through will regret it.
Erosion Control: Prickly Ash is naturally found in a wide range of sites, including ones with thin, poor soil. This, along with its propensity to sucker would make this a good choice for a slope or a bluff.
Restoration/Butterfly Habitat: Prickly Ash plays a natural role in ecological succession by colonizing old fields and pastures that are being restored into woodland, all the while supporting many forms of wildlife. If the thought of having a thorny, suckering tree taking over your restoration project gives you pause, consider this, Prickly Ash is quite intolerant of shade, once the oaks and hickories grow up the Prickly Ash will be shaded out, leaving behind a restored woodland.