A work area is an isolated area of the vault dedicated to changing a particular set of documents, such as a project. This is a little like withdrawing a set of master drawings from the print room, and taking them to the design office for the design team to work on.
Users working on the documents can access the work area and find the documents that are assigned to the project. In other words, a work area groups documents belonging to a particular project in a logical container, so that people working on the project can easily access the documents and users who should not have access to these documents can be denied access to the work area.