There are several different between a Company Account and a Subsidiary Account.
A Company Account, as known as, a parent account user (admin) will be able to create other admin accounts or subsidiary accounts (client account) for your colleagues. While Subsidiary Account user is only allowed to create a new account for same subsidiary level.
Parent account user (admin) may be able to overview all the credit unit purchase that own by this Company and Subsidiary Company. While Subsidiary Account user may only allow to view it's account summary in My Account.
Parent account user (admin) may also be able to publish job post on behalf of its Subsidiary Company by using Subsidiary's instant post units or its own units. While Subsidiary Account user can only look after its own units and job posting.