I have personally used the conversion chart myself for figuring out time adjustments to make when microwaving things. Like, I have a 1000 W microwave at home, but most everything is rated for an 1100 W one. Adjusting the cooking time really does help ensure the food cooks better.
The Microwave Cooking for One site is legit useful. You know that thing that happens when microwave food is half frozen? That’s not inherent to the microwave, it’s because most box microwave instructions are for 1100 watts and your microwave is something else. There’s a conversion chart for that!