In the government, committees are responsible to ensure that all the operations made by the legislative branch of the government run smoothly.
The tasks needed to be done in order to ensure this are really varied, so it is impossible for the same person to pay attention to all aspects of the operations.
Recuse of this, subcommittees were formed. Subcommittees would separate all committees' duties into smaller specific tasks and employ some people with suitable skill set to handle them,.