T&E is not really suitable for the outside environment due to it have low mechanical protection vaules E.g impact, vermean
Which are all really important when installing a cable in any location. Selection of the right install method and cable is so important
Notwithstanding, costs, customers budget, aesthetics, length of run, height on wall, direction wall is facing, (direct sunlight shade etc..)
etc
etc
FACT:-
a few meters of T&E run to a light fitting on a shaded external wall of a house will most likely last 20+ years without....
exploding.
electrocuting someone.
disintegrating.
tripping power from the whole installation.
looking excessively ugly or costing an arm and a leg!
a competent electrician should be able to evaluate the application of any accessory or cable he/she is installing..
and meet the customers requirements without going overkill on the safety.
whereas a long run low down a wall to a shed with 6+hrs per day of direct sunlight, would not be a wise location for T&E!
NOT all electrical work is 'Black & White'..
you can't do that but you can do this..
and if you do the other you must be wrong!!!!
Some T&E is at greater risk in the loft or under the floorboards from Mice, Rats, Squirrels etc...