What’s the purpose of doing this? (Site won’t load for me)
The goal is longer, thinner wings than usual. Long and thin wings are far more efficient—think gliders and the U2. But beyond a certain width, those wings become incompatible with existing airports and other facilities for handling commercial aircraft. So the idea is to mount folding extensions that are extended for flight, but likely fold when being hangered or navigating taxiways.
It was hard enough to convince a few dozen of the world's largest airports to make the alterations needed to accommodate the A380's wings. Demanding similar changes at the thousands of smaller airports where A320-class planes land would be a non-starter.
Perhaps similar:
One of the reasons the Vickers VC10 was so successful in the 60s and 70s was that it could operate from short runways, high ambient temperatures, and high altitudes compared to other jets of its era.
It was far easier for carriers like BOAC to fly those into Britain's former colonies than it would have been to magically expect all those colobnies to update their airports.
https://en.wikipedia.org/wiki/Vickers_VC10
p.s. As a boy, I flew to West Africa in 1970 on a VC10. Now I know some of the backstory.
Longer, thinner wings (higher aspect ratios) create less lift-induced drag for a given wing area, so ideally you want a super duper long and skinny wing, which will create less drag for a given amount of lift, and thus improve your fuel efficiency. Fuel is a massive portion of the total cost of operating an airliner, so there is a large financial incentive from the airlines to reduce fuel costs.
Unfortunately really long wings make airliners too wide to park at most airport gates, and in some cases too wide to taxi safely around obstacles, so they're experimenting with ways to make the wings fold and get a "best of both worlds" situation.
E.g. for the 777X it fits in Category E. Without folding tips it would be in Category F. Less gates can accommodate Category F.
https://skybrary.aero/articles/icao-aerodrome-reference-code
The second place was the XB-70:
The XB-70 was designed to use compression lift, a phenomenon also referred to
as Mach wave riding, which was demonstrated with the help of wind-tunnel
tests. It was shown to provide an increase in total lift at supersonic speeds
as wingtips folded downward, and would capture the shock waves generated by
the aircraft. Wing lift could therefore significantly increase by up to 30%
without any drag penalty.