Forbidden by purists, Chinese White is much more than a repair patch.
This semi-opaque pure white offers excellent permanence and a medium-high tinting strength. It's great for lightening other colours. Drop and spatter Chinese White into a damp grey wash to describe moist, mushy snowfalls. Employ a brush load of Chinese White where the water's edge meets snowbanks to indicate melting. For field flowers in spring meadows, a touch of Chinese White into Carbazole Violet helps create clover and other wildflowers.
And, of course, you can always use it to paint details and highlights! If the paint works, use it.