If I have a library that let me curry trailing arguments for a function, then I can see how something like std::flip() could be useful in letting me curry different arguments without costing extra lines of code. The library I had in mind is Google's RPC callbacks:
https://github.com/protocolbuffers/protobuf/blob/main/src/go...
This library was written in the C++98 era. It might seem silly now because with C++11, we could use std::bind or lambda expressions instead.