Built in shower- slab on grade

Starting here, and i could eventually provide a sketch if needed.

Getting near the ending stages of a house i am building. the whole house is polished concrete slab. The bathrooms are all exposed aggregate slab. All with radiant on 6" of rigid insulation.

Master bath shower is 4' x 8' all plumbing is roughed in. I have a 5' linear drain that will be centered.

Plan is to pour matching exposed aggregate for the floor.

My main question, given that this is slab on grade, is there any real purpose to installing a mud slab below the finish slab? its going to behave like a floor drain in a basement. does a mudslab do anything for me that i am just not thinking of?