Cache's importance in Drupal and what's new in Drupal 8

Drupal provides excellent content management tools to a site, but at the same time it requires a processing cost.
For static content sites where we can enable Drupal's default cache, much of that processing complexity is eliminated with page caching, and we need to concern ourselves only with the performance of the HTML page and its components. For this we will see some good practices as well.
But what if you can not use page caching? Like pages with dynamic content and authenticated user?

Let's review Drupal's Bootstrap phases, URL processing and theme rendering, and where the Cache fits in this context.
Some cache solutions such as page caching, blocks, custom cache, and some other solutions like AuthCache, Panels.
Through performance tests, how much improvement these solutions promote on the site's performance?

And finally, what Drupal 8 brings  in terms of performance and Caches, that promises to revolutionize Drupal sites!