Cellulose is the chemical name for fibre which is an important component of diet, even though it doesn't provide you with any vitamins, minerals or energy.
Humans and other animals, besides ruminants, cannot generate cellulase. They can break cellulase down only partially by using fermentation.

Cellulase enzymes are very helpful for the human body. Cellulase helps control sugar blood levels, by converting cellulose into beta-glucose, preserve an balanced cholesterol level and can support in lowering cholesterol. Cellulase supports in eliminating toxic chemicals, free radicals and other harmful organisms from cell membranes.
Cellulase breaks down and supports digestion in the fibre you eat

Most raw foods contain the very enzymes that your body needs to digest a particular food. For example broccoli contains cellulase to help break down the cellulose cell walls of the plant fibre.