When should the speed control (cruise control) be used?

You answered correctly. Cruise control should be used when traffic conditions allow you to drive at a constant speed. This typically means on clear roads, such as highways, where traffic is flowing smoothly and there are no frequent stops, curves, or obstacles. Cruise control is not recommended in heavy traffic, on winding or slippery roads, or where you need to adjust your speed often, as it reduces your immediate control of the vehicle. It is also not meant to be used only on slopes or only at high speeds; the key factor is the ability to maintain a steady speed safely. Following this rule helps improve safety and fuel efficiency.