"Yes, and" without the "and" is passive.

With the "and" it's active.

Not just acknowledgement, but building on it.

Without the "and" it just devolves into a distracted "uh huh, uh huh…"

The critical part of "yes, and" is the building on top of the most compelling part of what they said.

Even deciding what subset to build on is itself a creative act, an act of selection.