Need for an Implementation Package when creating a Change Package?

I'm looking for some detailed information why it is considered good practice to include an Implementation Package (IP Document) when creating a Change Package in eB. In 15.2.2 is was necessary to have the IP in order to navigate between the Change Request and the Markup (prototype). That is no longer the case in 15.4.1

I've created a Change Package that contains a CR and a Work Order but received some feedback that it is a good idea to include an IP as well. Why?