Again on the topic of icons, another article worth a read — with comparisons and examples from the original Macintosh HIG (Human Interface Guidelines) dating back to 1992.
In my opinion, Apple took on an impossible task: to add an icon to every menu item. There are just not enough good metaphors to do something like that.
But even if there were, the premise itself is questionable: if everything has an icon, it doesn’t mean users will find what they are looking for faster.
This is actually a good reference if you’re a product designer looking for mistakes to avoid.