At the time I bought the Y Strap I hadn't played guitar standing up for around 12 months, as I'd had tendonitis in my shoulder resulting in surgery.
Now I can play a couple of hundred gigs each year, all standing up! I use a lot of unusual playing techniques too like tapping and fretting upside down, so the weight of the guitar is not supported, but the Y Strap holds it balanced in place.
Now I could not live without it!