Here is a good explanation of microwaves, I prefer the inverter style.
Inverter vs conventional microwave: What's the difference?
It mainly comes down to the way power is supplied. In a conventional microwave a transformer turns the power on and off (you'll usually hear the microwave cutting in and out), which gives the food a chance to distribute heat.
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For example, if you set the microwave to deliver 50% power, it will actually go through cycles of producing 100% power followed by a period of no power to achieve the 50%.
In an inverter microwave, power is supplied through an inverter circuit to supply a steady and constant amount of power throughout the cooking time without cutting in and out. So if you select 50% power, the microwave will deliver 50% power throughout.
Not all foods should be blasted with maximum power in a microwave. Foods with high amounts of sugar and fat, as well as foods sensitive to heat like dairy, chocolate and meat (when defrosting) require lower power levels to effectively heat and reheat evenly.
Even if you're using a lower power level, heating delicate foods in a standard microwave can cause areas to overheat (especially around the edges) during periods of high power. Checking the manufacturer's instructions and recommendations will go a long way towards getting power levels right for different foods.
