In the graph, we can see that the more lignin, the higher the height that the plant can reach, that is because lignin makes the plants more rigid and provides support.
This is related to the need for more support, which is also a difference among aquatic and terrestrial environments, because, outside the water, plants needed more support than inside of it. For example, algae outside the water would lie flat, in contrast to the vertical position they hold inside the water.
So, the presence of lignin was crucial for the evolution of land plants.