I wouldn't go so far as to call that "practical." It's a cute trick, but it becomes really annoying when trying to write libpng bindings for any environment other than plain C.

PostgreSQL also uses longjmp to implement TRY/CATCH macros:

https://github.com/postgres/postgres/blob/master/src/include...

as someone who has used libpng I'd describe it as an example of why this is a terrible idea.