Why is diffusion important important to cells?

it allows for nutrients to come into the cell using passive tranport aka moving anything on a gradient without the use of energy (ATP).

Diffusion can occur across partialy permeable membranes, such as those surrounding cells. Therefore, diffusion is involved in the movement of important molecules into and out of cells. It is important for the uptake of substances needed by cells, and also the removal of waste products produced by the cells.