When only some things have icons, it's almost like a flag that these things are more special/useful/used. I think that is by far more useful than everything having an icon that you have to think about (or see the text next to it) to understand

I've seen some apps that have icons on menu items when those icons are used for the same functions in other UI elements (shortcut bars, etc.) that don't require digging into the menus, functioning as kind of a reminder that "you can do this elsewhere where you see this symbol". It is kind of like an inverse tooltip (where a tooltip you get by checking the icon and discovering the action description, this you get to by going to the action in the menu and discovering the icon.)

I think this is a useful pattern, but I'm not convinced that having specific distinct icons for menu items to highlight them as important is useful. Presentation order and/or simply a consistent difference in presentation for the highlighted items makes more sense.

It's pretty common that some things are more likely to be the things you are looking for than others. Drawing eyes to such things is helpful, whereas putting abstract monochrome line-art icons everywhere is not really helping anyone find anything.

Some things are only occasionally what you are looking for, and making them require a full scan of every menu entry is fine.

This has been my take too.

The thoughtful inclusion and exclusion of icons in menu items builds hierarchy. When every item is special, none are. You've lost the ability to differentiate.

Icons everywhere is a hallmark to me of "webby" UI.