Why would rapid cell growth be harmful to the body?

The body could produce too many cells and if too many are clustered together, cell communication, signaling, and transport of materials could be limited or even stopped entirely. Another reason is becuase the more cells andd individual has, the more risk for developing cancerous or mutated/harmful cells.

The body will have many cells, and it's better natural growth because the body is producing cells at his own "pace" and he knows what he's doing, while if you try to accelerate that it'll be harmful because of the amount of cells that the body will have.