It is the resulting turgor pressure on the cell wall that allows herbaceous plants to stand upright, and how plants regulate the aperture of their stomata.
The resulting decrease in cell turgor pressure and cell water potential creates the necessary water potential gradient that allows water uptake and expansion of the cell.
By loosening the linkages between cellulose microfibrils, expansins allow the wall to yield to the tensile stresses created in the wall through turgor pressure.