You have to explicitly set up an RP system to spit items out into the world. BC does that as the default "fail" operation. I'd rather have items keep bouncing around in pipes rather than spitting out at the first incorrect input. That said, it's easier to design a BC system improperly than an RP one in my opinion. If a BC system "jams" then you stand to possibly lose a lot of items. When an RP system jams, things just get stuck.. simply plop a chest on the line after the blockage to clear it out.