They are a huge difference maker, regardless if a pack is on your back or not. They take a lot of strain and stress off your quads, knees, hamstrings, calves, lower back etc. Great for balancing, aid in climbing give you control while descending, help to stabilize you or you+backpack.
Depending on the terrain and/or if I have been where I am going before they may or may not get used while hiking. Once an animal is down and I am loaded up, 100% of the time they are being used.