Even the smallest EC2 images can run multiple containers if your containers are small enough, and either way it makes sense to add a level of abstraction over y

Even the smallest EC2 images can run multiple containers if your containers are small enough, and either way it makes sense to add a level of abstraction over your pool of EC2 instances - i.e. treat them as pool as opposed a set of discrete blocks. ECS lets you specify exactly what resources each container needs, and then lets you make your pool shrink or grow as necessary. The pool can also be a heterogenous mixture of instance types, even a combination of on premise (?) ones. And could also be spot instances, which are way cheaper. Could also be whichever spot instance types happen to be cheapest at the moment. So yeah, being able to pool your EC2 instances is useful.