The thermals are already pretty bad in this device, so every little bit helps. At idle on silent with the dGPU at the lowest tdp and the CPU at 13w it idles at 55c. Turning off the dGPU gets it down to 45c. Repasting with PTM7950 gets it to 50c at 13w with dGPU on, 40c with dGPU disabled. Goes down a further 4c with the tape (assuming you aren't on a 0 rpm fan mode like silent).
Without the tape air is recirculation under the laptop. Air goes in and out the bottom without cooling the device. This wasn't a design choice to divert air over other components as there is foam along the edged of the heatsink that prevent it from going over the SSD.