I had my first experience with that yesterday. I'm using a Problem Solvers cross hanger. I love it. I assembling a bike with a new fork, stem and bars from what I have used. This clamp keeping the headset adjusted is gonna make getting the bars where I like them a piece of cake while swapping spacers around.

I don't know if one needs to or not, I put a 2.5mm spacer between the headset and the clamp.