Winglet removal.
Seem to remember that on a 747-400 it takes one guy with a spanner for the 3 or 4 bolts involved, and at least two with non slip gloves to hold the winglet and lay it down carefully on something soft.
But not in much wind, then it would be a hangar job.
Not much performance penalty but a lot of noise from press, when they notice. The DDM only allows for one at a time to be missing, when I asked around at Boeing why only one, the unofficial reply was that if you are that unlucky you should stay on the ground.