Smarty template engine: what is the difference between cache and compiled files?

Question

PHP

When initializing the Smarty template engine, you can set the path for caches, and the path for compiled files.

setCacheDir() and setCompileDir() methods.

What's the Difference? in terms of the contents of the files, they are almost the same, but what is their principle and what does each serve for?

and the second question at the same time:

also during initialization, you can set the path to the templates, through the setTemplateDir () method.
is it possible not to specify the path to the templates if my templates are rendered through the display method with the full path in the template?