I read somewhere that slip forming is how they made the legs of an enormous deep sea diving platform. They could not have made it any other way, just given the sheer size and the necessary construction parameters. The concrete foundation had to withstand the pressure of the ocean floor, so it had to be strong and seamless.
It weighs over half a million tons! And they towed it out to its present position in the ocean. It's the heaviest thing ever moved by humans, although admittedly the ocean must have taken some of the weight!