[jergason]

Also forces you to build your server-side stuff as an api, which makes it much easier for others to consume.

[rhizome]

Since there's nothing preventing the building of the API otherwise, this is really disabling everything but API access.

[awj]

In practice there is usually a world of difference between apis that are used to build a service's main website and apis that are written outside of it. Forcing yourself to use your own apis is one of the absolute best ways to ensure you improve it.