The "Other also bought" feature displays products that were also bought with the current one in some previous orders. If the feature is displayed in the cart, it applies to all products in the cart and shows products that were bought together with the whole order.
The "Related products" feature displays related products on the product detail. If the feature is displayed in the cart, it applies to all cart items.
This option shows "Related products" on the product detail only.

This option shows "Related products" in the cart only.

This option triggers the standard module behavior and shows Featured products, Latest products, Random products and Best products.

The parameters of the module can be set to a non-existing option. Be careful. The following example will not show any products at all.

It is highly recommnended to use the following script to create a new special position. Paste the following code into the your productdetail teamplate or cart template. The $position variable will be your new pecial postion for the module.
$document = &JFactory::getDocument();
$renderer = $document->loadRenderer('modules');
$options = array('style' => 'xhtml');
$position = 'extended';
echo $renderer->render($position, $options, null);