Ability to automatically scale with usage

Gone are the days of needing to overprovision a system with more virtual hosts than you typically need. As invocations ramp up, the underlying system automatically scales up, providing you with a known number of concurrent invocations. Moving this limit higher is merely a matter of making a support request to Amazon, in the case of AWS Lambda. Before this, managing horizontal scalability was an exercise for the team designing the system. Never has horizontal scalability for computing resources been so easy.

Different cloud providers provide the ability to scale up or down (that is, be elastic) based on various parameters and metrics. Talk to DevOps folks or engineers who run systems with autoscaling and they will tell you it's not a trivial matter and is difficult to get right.