When I worked on a grounds crew we cut down or pruned a lot of mountain ash planted as ornamentals. It was quite weak for climbing in, and as a wood, and especially prone to insect and disease damage. It seemed to be a favorite of sapsuckers here in the northeast, which usually ringed it with holes in rows - that definitely contributed to the other problems. It was planted for the colorful orange berries,
It is not related to the regular ash family. Just has "ash" in the common name.