Are the TSA's New Electronic Device Screenings Necessary?

First time accepted submitter Amanda Parker writes In July the US warned of a terrorism risk which led countries, such as France and the UK, to step up their security screening for flights to the US. Secretary of Homeland Security Jeh Johnson directed the TSA to implement enhanced security measures. In his statement on 6 July, Johnson warned that passengers could also be asked to "power up some devices, including cell phones" and stated that "powerless devices will not be permitted on board the aircraft". In light of the US Transportation Security Administration's (TSA) recent tightening of airport security to include stricter screening of electronic devices, is the TSA right to be cautious or have its actions caused unnecessary hassle for passengers?