This leads to cell and tissue specialization. This protects the organism from physical forces like the movements of air and water. This also insulates or buffers them from minor changes in temperature or moisture as well as nutrient availability. This also leads to larger organisms which can out compete other organisms for the resources available in the environment. Parts of the plant may survive attack by an herbivore or pathogen and can regenerate complete organisms.
Larger organisms tend to have longer life spans .
Multicellularity also lends protection to reproductive structures. It is inefficient for one cell to perform a multitude of functions. Consequently, cell specialization evolved.