The potential trouble is if the function pointer goes through a void* wormhole. (All of these types will be lost... like...)

In C you can cast a pointer, okay anything really, to a function pointer and then call it.

  int foo(int a, int b){return a+b; }
  void *vptr = foo;
  int (*yolo)(int a) = vptr;
  int c = yolo(10); // Cthulhu come

This sort of thing can happen when you pass a function pointer into some sort of callback mechanism+. When you get it back you have to cast it to the right type and then call it. So there is a disconnect between the cast and the function definition, unless you tie both together with a typedef.

+ Often helpful for an api that takes a callback to also record, who the caller was and some arbitrary bit of data. The arbitary bit of data might be a function pointer.