Sometimes I see pilots just walk around the aircraft, chatting, making selfies or just walking 🚶♀️ around prior to flight because they must.
Its a big nono! In fact we discover more defects during the exterior inspection (thats what the walk-around duty officially is) as during the rest of flight operation.
If the second in command or Pilot monitoring is doing that job on behalf of the Captain he is responsible for performing the task correctly and to report anomalies immediately to PIC.
This because its one of the most important tasks of aircraft accepance prior to flight duty and of upmost importance to flight safety.
Defects, leaks, signs of wear found can sometimes be allowd to dispatch the flight under the provisions of the CDL (configuration deviation list), which is the analogue manual reference for exterior defect as the MEL is for installed systems and equipment.
see yourself at discovering the issues published in Airbus Safety First newsletter.
(Internal Engine oil leak not indicated on flight deck),
(missing fuel panel replaced by a quick fix fuel cap),
(damaged stby pitot tube), etc...