
File Permissions are set when WordPress is installed. If you did not carry out your own installation, you may want to check that the settings are right for your site.
Setting file permissions for certain files may have significant security implications for your site. It is worth taking a few minutes to check your settings and make sure they match your requirements.
In short, an install done by an experienced WP installer probably won’t need any file permissions tweaks. A self-install might need checking. Also note that shared servers will need different settings. Personally, my sites are on shared servers, as I imagine the majority of WP sites are.