Regular commands: By default, all commands should be accessible in the Command Palette, must define a category, and don't need an icon, unless the command will be used in the Side Bar.
Side Bar commands: Its name follows a special pattern, starting with underscore (_) and suffixed with #sideBar, like _extensionId.someCommand#sideBar for instance. Must define an icon, and may or may not have some rule for . Side Bar exclusive commands should not be visible in the Command Palette. Contributing it to the or , we must inform that it will be displayed, and we can use terms "relative to other command/button" in order to you identify the correct to be used. Also, it's a good practice to define the condition () for the new command is visible.