What is the structural significance of 'dimples' on the fuselage of a Boeing 747? I recently watched the following video:

                
            

In the video there is a mention that there are 'dimples' visible on the fuselage of a Boeing 747, when it is on the ground. It then goes on to explain that once the fuselage is pressurised - the expansion helps to "smooth" out the dimples and it will be flat.

I am curious as to what the structural significance is for 'dimples' on the aircraft?
That's just oil canning of the unsupported areas of skin between stringers and formers, and when pressurized the skin stretches enough to remove them (18:00 in the vid).  The fuselage diameter will swell a little bit, maybe 1/8 or 1/4 inch, when pressurized.