If you're working on your theme, or if you changing module settings, and if you don't see your changes in front office - it's worth to clear shop cache. With this feature you can empty all cached files, so they will be regenerated and all changes that you applied will be visible. 

Cache . This option makes it possible for you to disable all file caches, and not just the one pertaining to template files. Only disable this if you debugging a theme or a module for PrestaShop. Otherwise, you should leave it enabled.
The "Clear Smarty cache" makes it possible to delete the cache in a single click instead of having to go delete files on your FTP server.