I may be mistaken, but aren't the larger EC2 machines priced fairly linearly with the improved resources? i.e. a machine with 2x the resources typically costs 2

I may be mistaken, but aren't the larger EC2 machines priced fairly linearly with the improved resources? i.e. a machine with 2x the resources typically costs 2x as much? If this is the case then can someone let me know the use case? Is this for better manageability? Or is it to overcommit (i.e. run 3x 4gb ram nodes on 8gb of ram). Other then that I can't see the advantage over dynamically spinning up & down nodes as required directly on AWS.