The Menu Item Assignment is useful for the times when you want to assign your box to specific menu items or to entire sub-trees of the menu item tree. This assignment is particularly powerful because of the fact that Joomla is very closely coupled with Menu Items. A fact which is apparent even when you want to create a module and you need to choose where and when it should be displayed.
In the table below you can see which options are available to setup the Menu Item Assignment
With this option you are presented with the entire tree of all your available menu items.
You are able to select from one to all of them just by checking the checkbox to their left.
Also, you are able to select entire sub-trees if you click the checkbox of a "parent" menu item such as the "Main Menu" as an example in the screenshot above.
|Include no Itemid||This option lets you choose whether you want the menu item selections that you checked to still be valid even when there is no ItemID parameter included in the URL. There are times that the ItemID is indeed missing and by selecting "Yes" for this option, the box will still be assigned.|
|Also on child items||This option gives you the chance to choose if you want the box to also be assigned to the child menu items of the menu items selections that you did. The expected behaviour would be "Yes" but naturally you are able to either exclude them or even include only them.|
You can imagine that the most common use case for the Menu Item selection is when you want to select just the homepage so that the box will not be displayed in any other places of your Joomla.