Why we need to consider minimum and maximum reinforcement during design for beams or slab?

the minimum are of reinforcement  is to control thermal and shrinkage cracking within acceptable limits.

also minimum steel area ensures that the reinforcement does not yield when concrete in tension zone cracks with a sudden transfer of stress to the rienforcement.

other hand,

the maximum is to acheive adequate compcation of concrete around reinforcement.

Agree completely with the answer above.

I also agree with the above answer