* They can specialize and perform specific functions. Different cell types in a multicellular organism need to express different sets of genes to carry out their unique roles. For example, a muscle cell needs to express genes for muscle proteins, while a nerve cell needs to express genes for neurotransmitters.

* They can respond to changes in their environment. Cells constantly monitor their surroundings and adjust their gene expression to adapt to changes in conditions like nutrient availability, temperature, or stress.

* They can develop and grow properly. Gene expression is tightly regulated during development to ensure that cells differentiate into the correct cell types at the right time.

* They can maintain homeostasis. Gene expression is crucial for maintaining the proper balance of molecules and processes within a cell, ensuring its survival and proper function.

* They can prevent disease. Misregulation of gene expression can lead to a variety of diseases, including cancer. Controlling gene expression is therefore essential for maintaining health.

In summary, controlling gene expression is essential for all cells to function properly, adapt to their environment, and maintain health.