Visible damage on a building, such as spalling brick, can be likened to a tooth cavity. If a dentist does not drill deep enough when he or she fills a cavity, the cavity will return.
Visible damage is frequently a sign of larger problems hidden underneath. Masonry is far too expensive to risk the damage coming back. Seven brick below the last visibly damaged brick should also be removed. They are damaged but imperceptibly so. Many times we need to go deeper than anticipated to complete the repairs correctly.
This is a large residential chimney where another contractor tore off the damage on top but stopped when the brick looked ok. They then rebuilt the top part again. Initially the chimney looked great, but in less than 5 years, the brick below where they stopped are now revealing their damage. The chimney already needs to be repaired again.