Heavy legs, happy spine. The belt takes the load.
Let the belt pull straight down on your hips, keep your torso upright the whole time.
Hanging the load from a belt around your hips means the quads squat against serious resistance while your spine carries almost none of it. The glutes assist out of the bottom as in any squat, but with no bar to stabilise, your legs get to be the entire story. It earns its place for stacking leg volume on top of heavy barbell work, or squatting hard on days your back has nothing left to give.
It can carry your leg training for stretches of time, since the squat pattern and quad loading are real. What it skips is the trunk and upper-back work of holding a bar, so most lifters use it alongside barbell squats rather than instead of them.
Anyone who wants leg volume without more spinal loading, lifters managing a beaten-up lower back, and taller people who struggle to stay upright under a bar. It is also a smart second squat late in a session when bracing quality drops.
At least to parallel, and deeper if the machine path and your hips allow it, since the belt pulling straight down makes depth easier to reach than under a bar. Use the handles for balance only, not to pull yourself up.
