>>149287822 (OP)Comic artists should learn how to do the lettering in order to understand about placement and reading order. Even if they don't do the lettering themselves (digitally or otherwise) they should have an idea of how much space to leave and where, so the letterer doesn't end up having to cover up important parts of the panel with dialogue.
That said, I have seen examples where the artist left plenty of space, but the letterer still decided to cover up the characters anyway.