Caching helps to deliver the content of any website faster. Scrivito already caches a lot of the data to reduce the number of API service requests. Even though most of the data is already cached, generating the actual HTML markup can still take a considerable amount of time. To further improve the performance and free up resources on the server, parts of the generated markup can also be cached.
Rails already provides several helpers for caching parts of a view or even the result of a full request. If you are not yet familiar with caching in Rails, you should read the excellent Rails guide on this topic.