I use 'em when I have to - if on the road and limited access to a real gym and I hafta get a lift at a 'big box' gym that day that doesn't have squat racks.
I used to use the one at my old gym for seated vertical presses and incline chest presses when I wanted to push to failure. But those weren't the only vertical or chest presses I did.
Wasn't important to me. It's not on my list of equipment to have in my home gym.
One of the trainers with whom I used to talk at my previous gym hated them, and never trained clients on them. He listed one reason why was, in his experience, they led to a greater chance of injury by limiting angles-/range-of-motion in the joints, IIRC?