I have watched some tutorials of creating custom post type. Some tutorials says when activating / deactivating the plugin you will have to call flush_rewrite_rules. But some tutorials did not mention it at all.
So is flush_rewrite_rules necessary when creating custom post type?
I have read the codex: https://codex.wordpress.org/Function_Reference/flush_rewrite_rules
it just says that it's an expensive call, but what will happen if you don't call the flush_rewrite_rules? I have backed up my .htaccess, after calling flush_rewrite_rules (where hard is set to true by default) the old .htaccess and new .htaccess are exactly the same.