PA28 airplanes have the intake in a heated part of the cowl that precludes icing. Carb heat will not normally be required as a preventive measure in this type of airplane, and it will reduce power, or even, under cold conditions, increase the carb temp into a region where icing is more likely.
Cessna airplanes, using the same engine, have their air intakes more directly situated so that they get colder air and therefore need the precaution of heat when in possible carb icing conditions. If you have a carb temp gauge, use the heat to maintain the temp in the green.
Cessna recommends the use of carb heat right to the ground, not just on approach. In really cold conditions (it is minus 25 outside where I am right now) we use (Cessna) carb heat all the time on the ground, except for the start up, runup and shut down, and only push it to cold after setting full power on takeoff (follow the checklist exactly). The idea is to get a good blast of hot air into the engine, not just for carb icing but also to help the gas to vaporise. An overshoot will be started with hot air, for the same reason. In some airplanes (carburetted) not using heat will cause the engine to stop since the cold conditions make it impossible for the carburetor to hold the correct mixture. Without heat it would be impossibly rich and the engine will stall on application of power. I have had them stop running in cold conditions when power is reduced to idle on approach, even with full heat, so I always hold a little power, and that way I know the engine is still running.
Too much heat can be bad too. A DC3 crashed in Canberra many years ago because the crew put the heat controls in full hot and both engines detonated themselves to death. Followed by the airplane and crew. Operating the carb heat might need a corresponding adjustment of the mixture. The Beaver will die on approach if the mixture is not adjusted with application of heat, especially in really cold conditions.
There is always more to learn, no matter how simple the matter appears at first glance. For example, how do you know you have carb ice? Or that you don't?