I did some testing today by plugging in a Core and Photon both connected to the cloud. Using the sensitive temperature sensor that is the knife edge of my palm, the Core is noticeably 2x or more warmer than the Photon. And the USB jack of the Core is even warmer as it’s tied directly into the heat sink of the LDO 3.3V regulator. The SMPS of the Photon is much more efficient and subsequently has less heat dissipation. The Photon also has some lower power modes that will drastically reduce heat dissipation if data can be communicated infrequently. Overall I would always recommend ventilation not knowing all of the circumstances, unless you can ensure the P0 module of the Photon remains under 60ºC in the max ambient temperature and highest duty cycle of network connectivity.