Multiple Enterprise Structures

My Client wants to have multiple Enterprises Strcutures within the same POD/environement. They are in the process of splitting out parts of the business to completely separate entities & therefore would like to have multiple Enterprise Strcutures with the same instance. In that context I need few clarifications

a. Do I need to use the task-> Establish Enterprise Structures to create Enterprises ? Do I need to list down all the LE, BU here ? Is this mandatory task ?

b. If I end up in creating 2 Enterprise Structures in the same pod, what could be the pros & cons ? Client is going to use all financials, FAH, Supply Chain, HCM modules