I've owned a few of these things for over 25 years, I have yet to use them

I inherited them from my youngest sister, they are light weight but I tend to shoot fast, sit and relax after on something nearby or the ground and soak up the atmosphere. I really don't want to carry anything else.
But if Barney takes his new De Vere out in the landscape he will definitely need to stop and regain strength every 5 minutes, maybe do some heavy weight training.
More seriously for wildlife shooting, trainspotting, where you you may have to wait patiently, they would be useful.
Ian