Soft limits protect against moves beyond the work area.
After homing, the app knows the machine's work area. It then prevents moves beyond the limits: jogging stops at the edge with the note “Limit reached”, targets outside are refused.
Switching soft limits
Settings → Machine → Soft limits switches this check on or off for the active machine. With a machine connected, the app can also set it in the controller ($20). This only happens when you confirm it explicitly. Grbl requires homing to be enabled for this ($22=1).