That only secures navigation on the main menu, not the item itself. Alternative navigation like context menus or kebab/sushi menus are unaffected, for example. There isn’t a way to audit all navigation methods so it’s really important to wire up security all the way down.
Related story, we switched to multi-site years ago and it was a long while Like 5 years before I realized that EVERYONE had access to Transfer Order… everything. Not the parent menus per se, as you all pointed out. But the app directly.
So if you add a new module, likewise get to locking down the new toys. Which could be in dozens of folders.