When you are going to create a configuration for a user, one possible approach is to start hiding the items that this user doesn't need. But what happens when we want to hide everything and just display a few items for that user? In would be a hassle to write item by item with a hide property. It is better if we hide everything and just show what we want visible.
If you are in a desktop device, you can go to your settings and activate a switch for Always hide the sidebar, so you will have the sidebar automatically hidden as in a mobile device. But if you are in a small-screen device, there is no Always show the sidebar option.
Home Assistant has a native feature to change the order of sidebar items or hide them. But this feature should not be used together with Custom Sidebar if you are using a custom order or hiding/showing items. So, in case that you are doing this you should disable this functionality.