Sure, my BJJ coach talked about relaxing to make yourself heavy, but then he didn't say how you could use that to connect your limbs to your center. I agree with much of Kevin Leavitt's comments posted later in the thread on this subject.
Something that was hard for me to grasp for a long time, but I am pretty decent with being heavy and using my weight correctly. My guys have a hard time with weight distribution and learning how to actively use it. Relaxing is not about being limp as you discussed above, there is active tension and active pressure being exerted where you want it. Put it in the wrong place you get a bad result. Get it in the right place and it feels like a ton of bricks laying on you. It actually feels like 3 or 4 times your actual weight. However, if you simply go limp and use dead weight, it doesn't work.
Again, not saying this in IS skills at work or anything, again, I am not about caring what IS is or isn't...but your comments on this hit home and is related since I can't seem to teach guys how to use their weight, pressure and relaxation correctly!