eBTax Party Tax Profile setup question

Hello Community.  We are trying to complete the setups in eBTax for Ireland VAT.  One question I have is what are the pros and cons of setting the option 'Use Subscription of the Legal Entity' in the Party Tax Profile configuration for Operating Unit Owning Tax Content as opposed to First Party Legal Entity.  Since the setting cannot be changed once done, I would like to understand which one is appropriate.

Thanks in advance.