What is an adaptive advantage of the large leaf like structure called a thallus?

The thallus is a large leaf like vegetative structure present present in the members of the thallophyta group. It is composed of the filaments. The size of the thallus may differ in different members of the group. It can be unicellular as well as multicellular. The one most important adaptive advantage of hauus is that if the member is struck in between rocks in the sea, the thallus can reach the sunlight better.