Postponing (often indefinitely) the need for scaling out your application can benefit you tremendously, not so much because of the instance costs, but primarily

Postponing (often indefinitely) the need for scaling out your application can benefit you tremendously, not so much because of the instance costs, but primarily in terms of reduced complexity in all aspects of development and operations. Also, for a SaaS, keeping the cost per served transaction low can mean the difference between making a profit or a loss in a market that has a converged on a price-point for a type of service.