The idea why cabin crew shall check with the flight deck before evacuating is so that a single flight attended might not have the full picture and inadvertently

The idea why cabin crew shall check with the flight deck before evacuating is so that a single flight attended might not have the full picture and inadvertently open a door close to a fire or similar. Which could severely reduce the time the airframe can withstand fire. The idea is to gain some situational awareness and only open those doors clear of obvious risks. The flight deck has for example access to ATC which can give them additional outside information that the flight attendants don’t have.