They use them when the lights are already strung up and they discover the strings are backwards. Not much fun unwrapping 1000 lights from an arch. It sometimes takes some convincing that running an extension cord along the string is much safer...
I have always said Christmas is the time of year when Santa comes down the chimney and the NEC rules go out the window.
Why do we need in use covers on every wet location receptacle but the 1-15 on the end of a string of lights can just lay in the snow? How many U/L stickers do you believe on those $1.99 100 light strings? (if the even bother) Running cords out windows from non-GFCI receptacles is very common.
But, single family homes really ought to have at least one GFCI outlet sited for festive lighting -- switched either manually from a floor walking height -- or via a clocked switch from a dry location -- as in heated, conditioned spaces.
This set up is needed for harsh weather -- and for the elderly.
Crazy risks are taken just to fire up light strings -- both electrocution and ice falls.
This kind of set up is a common as dust in my commercial prints. I can't recall of a shell contract that didn't have a provision for festive lighting.
It also wouldn't hurt if someone came out with light strings that were integrated with clasps that -- once mounted -- could stay on the building year-round -- and yet accept the light strings when lifted by a pole-grip -- all to get the public off of ladders in the dead of winter.
Every year the ERs of North America are stuffed with ladder-fall victims -- who were trying to place and remove Christmas lighting strings -- mounted via crude finishing nails tacked all along the exterior in the tackiest manner.