Impact of classifying org units/plants as IO instead of OU

We are working on global design for one of our clients. Client has got multiple org units/plants under one LE. We need to know impact of classifying units as Inventory organizations instead of OUs. 

One of the factors I wanted to have clarity is the impact on taxation and tax reporting if we classify a unit as IO and not OU. The key point to note is the impact from reporting perspective(Two Inv Orgs have two different VAT registration).  Also will there be a difficulty in setting up the rules for these units sharing the single OU. 

I guess the