What is an example of when you would increase friction purposely?
A simple one is on a vehicular race track. We need good-sized tires to get "bite" or "grip" on the surface to race. The F1 circuit features cars that have wide tires. The width of a pair of the rear ones is about half the width of the car. That's where the rubber meets the road, traction, which is friction that is intentionally applied.