Well I think for the clash sensor it makes sense to have it separate, so the user can choose where to install it, as position of the sensor greatly affects how it works in-hilt. I can only assume that the modularity of the daughter board is for a similar purpose; to make the installation that more, well, modular for the installer. I can see this being a benefit on say, a Parks hilt, where you might not have all your space available in one segment, and where it'd help to save even .25" in your main area of installation.
P.S. AG, I don't think IA is "putting on a show"; rather, he is reacting to your, lets say, um, direct, method of inquiry. Maybe next time, open with a general comment, then follow it with the question. That way the question might actually get processed and answered, and not seen as something kind of abrupt and/or inferring something negative. And the only reason I'm saying any of this is because I've noticed that this tends to happen frequently. Oh, and I think its safe to say at this point that most of us know you are studying engineering. When you keep bringing it up, and start rolling your eyes, and saying how "you don't need to be an authority on PCB layouts to see what I see", it sounds a bit pretentious. Sorry, but just looking out for you.