The Captain will order the evacuation including a command that specifies the exits to be used. For example "All Exits" or "Left Side Only" etc. The flight deck crew may have knowledge of a threat or potential threat that the Flight attendants haven't been made aware of. Obviously, the Flight Attendants will then assess their exits.
Carrier?
Why would the Captain dictate specific exits only to have the FAs make the call in the end.
Our FOM has the Captain making the evacuate command a d that's it.