Why do eukaryotic cells need to be able to turn genes on and off as necessary?

The reason why eukaryotic cells are in need of turning on and off their genes when necessary because of the reason that they may feel stress because they are under stress as they have the responsibility of acting immediately when they needed and by that, they need to be turned on or off in means of adapting to the stress that they experience.

i think it is true in my reasonment ..