ADA4817 Exposed Pad

My customers are considering ADA4817-1ACPZ.
ADA4817-1ACPZ has Exposed Pad.
The data sheet is "Can be connected to GND, -VS plane, or left floating."
When the customer selects "left floating", how many THERMAL RESISTANCE of ADA4817-1ACPZ?
Or should the Exposed Pad be connected to the PCB even when the customer selects "left floating"?

Best regards