Thanks for your response. I just did some net searches and the consensus seems to be that it does no harm to leave chargers plugged in. There is a concern about power usage but the Apple chargers apparently use very little wattage when disconnected from a device. Even so, there may be some waste.
However, my gut instinct is to unplug things when not in use. There is a possibility of something going wrong and of a short circuit or fire risk. Some people say plugging and unplugging causes wear and tear on the cord and is equally risky. A switched socket may be the answer.
You have had yours plugged in for two years and still going strong. I have had my iPhone for six years and its charger is still going strong with all the plugging and unplugging. Mind you, the cord looks a bit frazzled.😐