Let we see how the agile characteristic look like, if we use SharePoint as a framework to delivers use cases to our customer.
Set up time and cost: Installing the infrastructure, setting up the service applications, creating the first web applications and site collections.
Architecture limit: If limits are reached the architecture has to be extended or external systems have to be integrated like with the help of farms solutions or provider hosted apps. There might be a situation as the Architecture limit can be overcome only from Microsoft, which practically means that no delivery time or cost can be foreseen.
Figure 1. Agile technology curve for SharePoint