Q: or do you tend to leave that for / change it up in production (examples appreciated)
A: the first example that comes to mind, to explain this, is not my song, but it's a good example to explain it: if i were writing the song Africa (by Toto), i'd say the huge drum fill just before the chorus, that would be something written into the song. because that's something that takes the lead at that moment. if you were singing that song to a friend, you'd almost certainly have to sing that drum part there. it's a feature. but anyway, here are some examples from my own songs, of things that were written, or not: