Twilio summarises it nicely

Twilio,  a silicon valley “unicorn” has filed for an IPO this week. From their S-1 filing paper:

The way organizations build, deploy and scale modern applications has fundamentally changed. Organizations must continuously bring new applications and features to market to differentiate themselves from their competitors and to build and extend their competitive advantage. Heightened consumer expectations for real-time, personalized interaction further necessitate rapid innovation. In order to satisfy these needs, developers must be empowered to freely experiment, quickly prototype and rapidly deploy new applications that are massively scalable. Legacy infrastructure does not support this new paradigm for developers because it typically has been slow, complex and costly to implement, and inflexible to operate and iterate. 

We could not have said it better ourselves