|Quoting FlyMIA (Reply 2):|
Well I have no idea what those things are for, maybe for mechanic checks? A D check where they take everything apart maybe that's how they hold the wings?
Life rafts mainly, but I have seen them used as anchor points for mechanics safety harness, when you are working close to the trailing or leading edge with some or all of the flight controls removed. For the most part they are there for the mechanics to trip over when working on the wing.
The airplane is usually on jacks during heavy checks, and if there is major structural work being done usually the fuselage is jigged, and jacks in place so nothing moves.