What are the advantages for an organism to have tissues instead of the one type of cells?
A tissue is made up of several cells that are similar, have the same origin and can carry out a similar function. It is a higher organisational level where cells group together to perform a similar, bigger function. For a cell, as a single unit, it would be difficult to perform complicated functions. Tissue is a significant example of how species have evolved. Unicellular organisms do not have tissues nor do the simplest multicellular species such as sponges where tissues are poorly differentiated. This makes it clear how the functions performed by such organisms differ from those in plants and animals where the system is more organised.
When an organism have simple functions it may have cellular organisation but as it's functions become complex it's cells differentiate to do different functions and cells come together to form tissues and organs and thus organ systems which help the organism to perform different functions easily thus if higher organisms will have cellular organisation it will become difficult for it to perform it's many functions