This chapter is not intended to “rewrite” the official documentation, but rather to shed light on how low-level « cache-block » functions work, on the associated « template-block » caches, as well as on the impact of various settings tweaks on the performance of a website.
The « cache-block » are the template functions for declaring a portion of the template to cache
The « template-block » are the result of this caching, ie the storage mode of thise cache in {VarDir}/cache/template-block/... (a specific chapter details the storage mode)
What's the purpose of the view cache?
The « cache-block » manages cache of the « portion of static xHTML page » type, otherwise known as the « template-block » where the view cache does not allow it, such as:
Caching « parts » of the pagelayout.tpl and its alternatives (override template, or via the layout module), for headers, menus, footers, etc.
Caching « parts » of native module templates (which have no view cache) other than « content » and its $module_result.content
Caching « parts » of a custom module templates (which has no view cache), for example to cache each node in a result list
Caching « parts » of templates of any templates, even those already subject to the view cache (a marginal practice but an interesting and sometimes too discredited)