Hi,
don't know if I'm misunderstanding your question, but you asked what types of business need networking... based on the assumption you are talking about inter-company networking (and not network requirements within the business - if this assumption is wrong and you mean systems, change the word "business" in for the rest of this post to "system") the types that interact through process and/or (more likely) data.
What types of business would that be - from a theoretical perspective all of them as all businesses interact with (at least) customers and optionally (but usually) suppliers.
From a real world perspective those businesses requiring networking are those that are not constrained to only unautomated interactions with customers and suppliers. So any automated interaction with an organsiation external to the business needs networking. Thus internal processes such as internal audit, timekeeping etc have no networking requirement.
Hope this helps and if I am still misunderstanding the question, yell at me!
Guy