Locusts do make good hedges, if you mean hedge in the old English sense of the term. In old England farmlands, hedges were planted, nurtured and maintained as fences to keep livestock within boundaries. It didn't matter what the trees looked like. It only mattered that they worked—living or dead—to restrict the movement of animals. And because they are both strong and rot resistant, locusts, especially when they have thorns, can do a good job as fences even when they are literally pruned to death.
But then there is another type of hedge. This hedge is ornamental, which means that it is more important how the hedge relates to your eyes than to your skin. Ornamental hedges provide a visual emphasis to borders of all types. Many times, hedges have been effectively used to hide ugly foundations. Other times, they have served to accentuate separations: a lawn and a street, a lawn and an enclosed garden, my property from yours, etc. These hedges are typically sheared to produce a formal, linear shape. Most hedges don't reach much higher than the scale of a human either, because privacy, or visual impact only needs to be oriented to the realm of human—not drone—vision.
The point is that shade trees are appropriate for the first, narrow use of the term hedge, but not the second.
Look at the photo. I have been on several tours of the inside of this church for art and architecture, and I have marveled at how extensively and effectively it utilizes and preserves the now-nearly-timeless art and architecture lexica effectively to communicate. But recently the landscape outside of the church has received some maintenance that is outside the arboriculture lexicon. In other words, the locusts planted alongside the church have been treated like a hedge. And the resulting hedge is neither a fence nor a human-scaled separation accent.
It is possible that branches from the locusts were beginning to invade the building. Shademaster locusts will spread 40 feet wide at maturity. So a "tree guy" was probably hired because the trees were "getting too big." But look up and out in the photo. There is nothing above or on the street side of the trees, so no reduction was needed there. The only pruning needed was directional: off the building.
Instead, in an instance of extreme irony, the maintenance of the church trees broke a transcendent rule: "Do not leave a cut at the end of any branch." The tree doesn't know who cut it or why, but the cut sent a biological message which every tree will obey: "Double your efforts in that direction." So while directional pruning would have been a long-term solution, the tree guy now has job security. He will have to come back soon to maintain the hedge he has created.
Joshua Arp is an ISA-certified municipal specialist, Clarks Summit's municipal arborist and an operator of an organic lawn and landscape maintenance business. Reach him at firstname.lastname@example.org.