From Paul Mullin's Blog Just Wrought comes this 2010 interview:
MULLIN: How crucial do YOU feel an early, robust relationship between playwright and designer(s) to be? I.e. am I full of shit and if so, why?
MATTHEW SMUCKER: An early relationship seems like a swell idea. But in my experience, it isn’t the typical model of how plays get made. My primary interaction is usually with the director, who serves as a conduit of playwright’s vision but often also as a buffer. They are the chief interpreter, whether they fancy themselves auteur or consensus builder or cat herder or usually somewhere in-between. The times when I truly have felt the “early, robust relationship” with a playwright, it has been with a playwright directing the play they have written/are writing. And this has been great—I see my responses to early drafts (or to source material, if it is an adaptation) mutate and become fully integrated into the final creation. The play on stage is better because the collaboration is deeper. If the hypothetical playwright and director are separate individuals, it seems like the real robust relationship that should be proposed is not just playwright/designer, but rather playwright/company. In this case “company” constitutes all of the interpretive artists—director, actors, designers. The playwright isn't just writing for an abstract actor/director/designer, but with them.
Read more of the interview, as well as thoughts from designers Etta Lillienthal and Gary Smoot here.