There are a couple of key factors to consider when considering this situation. They are: what is the functional currency to be for each of the companies, what are the financial years of the companies and will they have the same chart of accounts and analysis structure.

If the answer to any of these is that there are differences between the companies then it would point to setting up the different companies as different business units, so as to allow for the different key definitions.

If the answer to these factors is that they are the same for the companies then there are two possible options. The most common option these days is to set them up in a single business unit, with a transaction dimension defined for company code. The business unit is then configured to ensure all journals/transactions balance at the company level (hence ensuring each company has a balanced ledger). Benefits of this model is that it is easier to maintain and ensures consistency of structure across the companies.

Alternatively the less common option is to set the companies up as different business units and maintaining separate sets of records for each. The primary weakness of this is the time and effort required to maintain them (everything has to be repeated across the companies) and as such keeping the companies data structure consistent.