Colonial organisms (organisms that form colonies) are hypothesized to have led to the formation of multicellular organisms, according to the colonial theory. All the plants, animals and higher life forms are multicellular (i.e. consist of more than one cell) in nature.
Identical organisms group together to form colonies for mutual benefits (security, food access, etc.), much like human beings. Haeckel, in 1874, proposed the colonial theory, according to which multicellular organisms developed as a result of colonial organisms forming colonies. For example, Salpingoeca rosetta (a bacterial predator) form rosette-shaped colonies and this enables them to capture bacteria more efficiently. It is hypothesized that organisms (such as flagellated protist) form colonies and by selective reproduction of individual organisms evolve into a tissue (or a multicellular organism). Colonial organisms are supposed to have developed around 1.5 billion years ago.
Colonial organisms are things like corals and the like.....things that live in colonies.
The benefits of colonization greatly outweigh the possibility of survival of individual species because of increased reproductive success among other things. (less space for things to get lost in).
Organisms evolved as single cells, with time they evolved into multi celled organisms. Colonial organisms can be viewed as something in between. Able to successfully survive on their own, but better survival when amassed as a colony.