Idea is to have different cut in and cut out temperatures. In most cases it does not matter if temperature is sport on with accuracy of 0.1 degree specially for hot water.
If you have deadband for active set-point you check if temperature is < set-point – deadband to start zone and you check that temperature is >= set-point+deadband to stop zone. This way you don’t cut in/cut out that often.
This approach is used if you know that you are ok with lower accuracy and you don’t want to ware out equipment that fast by starting/stopping heating.
If you still want to have accurate temperature to 0.1c you can set deadband to 0.
For more info about deadband refer to wikipedia link