The idea originally came from a requirement to find a more cost effective way to transport semi-submersible drilling rigs to different locations round the world.
Heavy weather is not a problem, that is addressed in design of grillage and seafastenings. Routes are carefully worked out and alternative safe-havens are identified along that route. Prior to departure everything is checked and the vessels in the towing spread and the heavy transportation barge itself receive weather forecasts, looking five days ahead, at minimum 12 hour intervals from at least two independent sources.
Equally impressive are the heavy lift barges, biggest in the world is Saipem 7000, a dynamically positioned (does not need anchors to stay in position) semi-submersible barge equipped with two 7000 tonne cranes allowing a tandem lift of 14,000 tonnes.