Sometimes you need to render a line item in the cart differently than the rest.  

A sample usage case would be to prevent the quanity of a cart item to be changed.

A built in feature of the cart rendering, is the ability to render each product type with a different template. 
You can define the template via layout xml, using the "addItemRender" action within the 'checkout.cart' block

However, it is impractical to go an create a whole new product type. This article show another, very very easy way