The simple answer is yes, you can technically microwave aluminum foil, as long as the manufacturer clearly indicates that your model can handle the foil in the device's manual. However, there are specific conditions that need to be met. Most importantly, the foil needs to be kept as flat as possible. When foil is bent or wrinkled, a phenomenon known as "arching" occurs.
Microwave safe simply means that the material won't melt, crack, or warp in high heat produced by a microwave, which can reach up to 212 degrees Fahrenheit. As long as the container remains intact, you're technically in the clear. The term doesn't account for less visible risks. From a regulatory standpoint, there's no universally enforced standard for what makes a container safe for the microwave. Container makers often decide for themselves whether the product merits the label.
One argument for unplugging is phantom or standby power. Not unlike why you should unplug your toaster, many devices sneak electricity even when they're off. Government energy experts note that this standby draw adds up across a home and suggest reducing it where practical by unplugging, using advanced power strips, or choosing efficient models. Microwaves are among the products that can draw power for displays and ready-to-start electronics.
A microwave's main purpose is convenience. It boils the meal-prep process down to the least amount of time and steps possible: Simply heat and eat. While we hate to potentially burst this bubble, nothing is more important than safety. You might want to add just one step back into this routine by switching whatever you're microwaving into a different dish or bowl if you're not 100% sure that a container is, in fact, microwave-safe.