Fold as a tablet is really useful for multi-tasking. But for watching media not much different from regular phones due to the huge black bars. Flip phones I guess are useful for people who want to fit their phone in a small pocket. Personally, I don't see any usefulness from either type of phone. Nevertheless, the tech is indeed great.
From a technical standpoint they definitely don't offer any objective advantage. However I still love using them personally. There's just something satisfying about folding your phone. Also the built-in screen protection.