On the trail, maybe.

But when you are in your house, what advantage do they have over cooking from scratch with actual ingredients?

Pasta, beans, couscous, meat...can all be cooked the same way you're heating water for your dehydrated meal.

They're much easier to cook. Pour hot water in and wait a few min and that's it. If you were to make pasta, sauce, toppings, meat etc. individually using only boiling water, it'd take quite a while and probably not taste very good. But I guess if the power's out and you're not working or anything, time isn't really an issue?

Shrug. Just tradeoffs between cost, time, health, convenience, and taste, like most food.