Inventory Organization - Fundamentals

HI All,
This question might sound obvious but want to get the fundamentals clear i.e. in which scenario should we define an Inventory organization?

Scenario1:
I have a warehouse at a particular location which stores my inventory. In this case should I go ahead define an inventory org and then define warehouse as a sub-inventory.?

Scenario2:
In telecom domain, we have network service provider who choses a site to install network related stuff. In this case should I define the site as a sub-inventory ? Or should I define a new inventory org?

Any inputs please?

Regards