New company or process levels within existing?

We are adding 4 small "companies" to our exisiting Lawson population. We were planning to set up 1 new company (because that has been the practice) with 4 process levels, but I wonder if that makes sense. All 4 of these new groups are actually part of the existing Company 1 organization and each has a separate tax id. Any thoughts on pros/cons of creating/not creating a new company for this? Thanks for any input!