reason is performance. The browser is trying to _save_ you from the cost of parsing functions that are never invoked. If you have a function like: ```js function doNothing() { console.log('do nothing!'); } ``` Then if you never call `doNothing()`, the browser can avoid fully parsing it, which means it can avoid the cost of allocating the function object, setting up its scope, etc. This is a good thing! That's why `optimize-js` only focuses on the functions that are likely to be invoked. ### Does this affect run-time performance? No, this only affects the initial parse time of the script.