As well as the usual reheating food in the microwave, I use it a lot.
I defrost meat when I have forgotten to take anything out in the morning. Keep it loosely wrapped though. Two slices of bread are removed from the pack in the freezer, put in a cellophane bag and defrosted for 30 - 40 seconds for sandwiches.
I don't use it for anything that needs regular stirring, like porridge, scrambled egg or sauces because it's too much faff to keep opening the door.
I particularly use it for poaching fish, and all fresh or frozen vegetables.
I have a range of dishes with lids that are used all the time. The glass pyrex ones are perfect but the plastic ones (designed for cooking not just reheating) are invaluable.
So, when poaching fish, I use the largest pyrex dish, cover the fish with milk and cook on medium for a few minutes. The milk is drained off for the sauce and the fish is kept warm in the dish with the lid on.
The largest pyrex dish is also used for making mashed potato. The potatoes are chopped into smaller pieces than you would normally, cooked in a small amount of water until soft. The water is mashed into the potatoes so no vitamin C is lost, then I mash in a knob of butter or margarine and any seasoning, after that I add milk to the desired consistency. Because the milk is cold from the fridge, the whole lot is then reheated with the lid on, for two minutes in the microwave before serving.
Frozen vegetables are cooked straight from the freezer in a dish with the lid on. No extra water is needed so no vitamins are lost.
Fresh vegetables are all cooked in a dish with the lid on in a small amount of water.
Any water that appears from cooking frozen vegetables and all the water used in cooking fresh vegetables are drained off and added to any sauce, gravy, stew etc.
So cauliflower cheese tastes amazing because all the cooking water goes into the roux before adding milk and cheese.
I have been doing this since microwaves came out so I have got used to juggling and coordinating what's being cooked as the same time as whatever main dish I am doing on the cooker.
The key is to always cover everything appropriately with a lid or a piece of kitchen paper and not to overcook anything.