Hot rolling occurs above the recrystallization temperature, which makes the steel easier to form but leaves a scale surface and looser tolerances. It is the economical choice for structural sections, plates and large pipes.
Cold rolling follows hot rolling with further reduction at room temperature. The result is a smoother surface, tighter dimensional control and higher yield strength through work hardening.
Choose hot rolled products when strength per cost is the priority and surface appearance is secondary. Choose cold rolled when you need precise dimensions, a clean finish for painting, or thin gauges below what hot rolling can hold.