You'll get 5 free instances if you get a subscription, but that kind of messes with the whole "just install Ubuntu from a USB key and use it with no hassle" workflow many Ubuntu users used to love.
It only matters if you want support after 5 years. Just upgrade to a new release if you don’t need 10 years. If that’s a hassle, get the free subscription for 5 machines and you get 10 years.