I would guess that most people usually just use the highest (and default) power on their microwaves but here’s a poll anyway. If you do vary the power, when do you do it? I’ll put mine on 50% when reheating steak in an attempt to keep it from overcooking the meat.
How often do you use less than full power?
Only if I want to defrost something that’ll take a long time to defrost. Then I’ll put it on lowest power for like 20 minutes.
I often use lower settings.
Ever microwave something and you find there is one hot spot surrounded by cold spots?
A lower power setting usually just turns the microwave on and off. This gives the heat more time to spread to the cold spots. Sure it takes longer but it’s just a few minutes.
I run it fairly often at other power settings, but that’s mostly when I know it’s something that will heat a lot on the outside, and need time to distribute that heat. That’s why the microwave instructions on many things specify a sit-time at the end of the cooking. It gives that heat some time to conduct through the food and reach some sort of equilibrium.
Microwaves typically run at full power, and the power settings are more of a percentage of the time it’s “on”. So it makes sense if you’re cooking something larger or dense, that you might want to bake that sit-time into the cooking time. So for example, 4 minutes at 50% is the same total power output as 2 minutes at 100%, but the 4 minutes will end up more evenly heated because you’ll have essentially had two minutes of sit-time built in.
I would say that I rarely use the high setting. Maybe if I’m boiling water or cooking something that can’t overcook, although I can’t think of an example right now. For most things I use a lower setting to ensure that it heats more evenly throughout its bulk.
I use a very low setting (which, as noted, is really two or three seconds “on” followed by seven or eight seconds “off”) to reheat something for twelve or fifteen minutes more often than I hammer something on high, actually.
This.
All reheating is at 50% or less power.
When I poach eggs, which is nearly every time I make breakfast at home, that’s at 50%. Makes much better eggs; New and Improved! Now with far fewer explosions! 
Full blast is used every day for 2 minutes to boil water preheating my coffee cup, then again for 30 seconds to heat the cold cream in the hot cup before the coffee is added. But that is the only use I have for full power.
I use the reheat setting for making cocoa since it’s less likely to scald.
That’s not true for inverter microwaves. Instead of cycling full power on and off, they actually deliver a lower power continuously. I love my inverter microwave and wouldn’t go back to the old style, even though the inverter models tend to cost a little more. (I know you said “usually” so I’m not saying that your statement was wrong.)
The popcorn setting is the only other button I consistently use. Once In a great while I will defrost, but I generally buy my meats fresh or thaw things out in the morning for dinner.
When I make a bowl of oatmeal I use 2 minutes at 80% power. I’ve discovered that gets it hot without overflowing the bowl.
Does that really change much though? I mean, 3 minutes at 75% is the same output in either case, and you still have that extra 35 seconds spread throughout for the heat to distribute either way vs. 2:25 at 100%.
I think it depends on how fast the heat propagates through the material being heated, and how sensitive the material is to overheating. If you heat at 100% for 15 seconds, then turn off for 15 seconds, and repeat that, it’s true that the total output is the same as heating at 50% power continuously. But say you’re trying to get the whole thing to 160 degrees. During that 15 seconds of full heating, parts of the material might overheat to 200 degrees, then during the 15 seconds off, the heat redistributes and the hot parts cool down. Maybe the end result is the material reaches 160 degrees in both cases, but in the cycling case, parts of the material got much hotter than you intended.
If I were ever heating something whose directions said to use a different power, I would poke around in the settings until I figured it out. As it is, though, I don’t even know how.
This used to be true, and in fact you could find plenty of sources that said that it was physically impossible for a microwave power level to change any other way. But nowadays, actual changeable power level is pretty common. I don’t know if it makes any real difference compared to the strobing method, but it’s advertised as a selling point.
Many of the things my wife and I heat for lunch have directions to use 70% power (it’s almost always 70% for whatever reason) so that’s what we use. I sometimes try to use lower power settings when reheating things but I’m not always the best at guessing how long at what percentage.
This. When I make oatmeal with regular oats, it takes about 5 minutes once it’s boiling, at about 40% power in my particular oven, to cook it without boiling over.
I very rarely will defrost a piece of meat. Maybe 40% power, watched carefully.
Off the top of my head I couldn’t tell you how to change the setting off of high. I know it’s possible and I’ve done it but I don’t remember now. I would only use the lower setting if whatever I was heating had directions that said to do it.
Microwaving on max is kind of like trying to heat food with a blowtorch. The outside gets a lot of heat which takes a while to get to the inside. Max works fine for stuff that’s liquidy or will transfer heat easily, but some stuff like frozen food will be overcooked/rubbery/dry on the outside by the time the middle is warmed up. For frozen entrees I’ll do a 50% or less power for more time. Oatmeal I do at 50% so it doesn’t boil over. Defrost will be at 10% or so. Reheating dense things like a baked potato or meats I’ll do at 30%. Meats especially can be adversely affected by high heat. High temp can cause the fibers to contract and squeeze out moisture, which makes it dry and rubbery. Lower power will heat up the meat slowly so that it retains more moisture and tenderness.
Every time I need to melt butter, which is every couple of weeks at least. I made crepes this morning so I had two tablespoons in for 3 minutes on 2/10 power.
I also do my oatmeal on 7/10. I can see it boiling over and kill it before it explodes.
Also some frozen foods say to defrost on medium.
Every now and then I buy something frozen that has directions involving other-than-high; e.g., Rao’s penne vodka says to use 100% power for 3 minutes, partially remove the film, stir, re-cover, and use 50% power for 3 minutes. Even though 1.5 minutes at 100% would likely make no noticeable difference, I do as they say.