local plant depos have these on their water lines; most of them are old and broken, so it would seem at one time it was thought of as a good idea, occasionally i will see a one on a camper van build.
i always just assumed it reduced natural eddies for water moving in a pipe reducing erosion inside the pipe lowering containments. A river travel straight for 10x its width before turning because of coastal drag and eddies overcoming inertia.