Hi @babydu,
We structured the plugin such that you should see no difference in performance when compared to loading the same code from a child theme. All snippets are preloaded efficiently.
WPCode can do a lot more than simply adding code in the same way you can in the functions.php file but one important benefit, if you already have a child theme, is that if your code in functions.php throws a fatal error you will have to go through FTP to update your file while WPCode has error protection built-in and even in the rare cases where WPCode can’t catch an error you can use the WPCode safe mode to immediately update your code directly from the admin.
On top of all that, WPCode comes with built-in Auto-Insert Locations and Conditional Logic that reduce the size of the code that you have to maintain, and, you can also add non-php snippets for HTML, CSS, JS directly from the admin without having to write the logic for those in the functions.php file.
Let me know if I can provide more info.