This is the maximum to which a helium-filled core can grow, and if this limit is exceeded, as can only happen in massive stars, the core collapses, releasing energy that causes the outer layers of the star to expand to become a red giant.
This threshold represents the maximum size to which a helium-filled core can reach, and if surpassed, which can only occur in extremely massive stars, the core undergoes a collapse, resulting in the release of energy that leads to the expansion of the outer layers of the star into a red giant phase.