I have been wondering about the necessity of my sternum strap. On my external pack, it was the first hing to go, but now I am moving to an internal frame and am reluctant to remove it. While hiking, I find the strap restrictive, and sometimes it is difficult to breathe with it on (no matter how loose). I believe some of it is psychological, but not all. How many of you use a sternum strap? How many don't? Can it be useful in certain situations (to the point I should leave mine attached)? Thanks for the input!