Well, there is a middle ground: when you haven't written that big framework/engine, but could have, delving into the source code in an as-needed basis may sound

Well, there is a middle ground: when you haven't written that big framework/engine, but could have, delving into the source code in an as-needed basis may sound like a decent option. Of course, you're hoping your framework is fit enough for your purpose, so that you rarely have to inspect it —if at all.