The primary purpose of cruise control, when activated is that it enables you to maintain a minimum speed of approximately 25 MPH or higher without keeping your foot on the accelerator. This can help reduce driver fatigue during long trips.
But cruise control can be dangerous if used on winding roads, in bad weather or in heavy traffic.
Your cruise control does not know the difference in road surface types. This makes having it activated dangerous on slippery roads. Unless it is deactivated by tapping your brakes or disengaging it, the vehicle will not slow down during a skid.
There is a potential problem with the use of cruise control on wet roads. Particularly where ruts cause significant standing water buildup, leading to hydroplaning at lower speeds. When the drive wheels start to spin due to loss of traction, the electronic controls will reduce the throttle setting to compensate. When the wheels leave the water and regain traction, they will be going ‘slower’ than the cruise control setting, and the computer will now apply the throttle to accelerate back up to the set speed.
Depending on the road surface (hills, curves, etc) this acceleration may not be appropriate for the roadway. The driver may now have to react quickly to restore the desired speed, path, etc. Under severe circumstances, in the short time this takes, the driver could run into control trouble, run off the road, etc.
Keep in mind that emergencies are all about time and distance. It takes the “Average” driver .5 seconds to bring their foot up off the floor to the brake pedal and disengage the cruise control can be crucial. If while on cruise control the driver’s foot is on the floor, that number would be significantly longer.
To put this in perspective, at 40 MPH, in .5 seconds, the vehicle would travel 30 feet before the driver could disengage cruise control. 30 feet in a vehicle losing control is a long way to travel.
In heavy rain or on problematic road surfaces it makes good sense to be prudent and switch off the cruise control.