Developing with dispatcher in mind - non-cachable content

[boser87]

Hi,

I am watching this video about developing with dispatcher in mind: AEM Dispatcher

At some point of the presentation one statement is: "Follow the AEM model, non-cachable content should be served dynamically from a restful service, layout should be delivered from cache". I actually did not get it.

Why non-cachable content should be served dynamically from a restful service? Examples?

What does layout mean in this case?

Thank you!