[derefr]

That's a different kind of thing—TLS is an extensible protocol, where its various extensions (i.e. code paths) are activated by patterns of data on the wire. libsodium is just a set of components—you can know at compile time exactly which functions in libsodium will or will not ever be called by your program, and can, if you like, use a linker that does LTO to prune the majority of the library out.