They are some of the fluid transport mechanisms necessary for life.
Capillary action is really just a specific example of surface tension. Surface tension is the result of attractive forces between liquid molecules – most often water in biological systems. This ‘tension’ can become a force for motion, as in capillary action.
That is the mechanism of liquid delivery at the smallest scales of biology – plant sap carrying nutrients, blood carrying nutrients in and wastes out of an organism. Without it, living organisms would look and behave quite differently, if they existed at all.