What the forms are actually controlling
A form is not just a wall to keep concrete from spreading. It sets three things at once: the outline of the slab, the thickness, and the slope that carries water away from the house, garage or shop instead of back toward it. Get the forms wrong and the slab is wrong, because whatever shape, depth and fall the forms hold is what you are going to live with once the concrete sets.
Straight runs get straight forms, staked on a line. Curves, like a circular drive or a rounded patio edge, get formed with material that can hold a bend without kinking. Either way, the form work happens before a single yard of concrete is ordered, because it decides the yardage.
Why forms get staked as hard as they do
Wet concrete is heavy, and a loaded chute puts real pressure against a form as it fills. Forms get staked hard enough that a full pour cannot shove them out of line partway through, because a form that moves during the pour changes the shape of the slab while the crew is trying to finish it. Getting the stakes right before the first truck shows up is cheaper than fighting a bowed form on pour day.
That staking matters even more anywhere the pour runs through a line pump instead of straight off a chute, because the hose is placing concrete at a steady, continuous pace rather than in the start and stop rhythm of a chute pour. Forms have to hold their line through that whole steady pour, start to finish.
When they come off
Forms stay in place through the pour and the finishing that follows it, then come off once the edge of the slab is firm enough to hold its shape on its own, usually within a day or so. After that the edges get backfilled and graded, and the forms leave the site with the rest of the job debris. A light form line along the edge is normal and is not a defect.