Members of Parliament are very busy people and do not need to be present in the House of Representatives or Senate at all times while their chamber is meeting. They may be at work in other parts of the building, such as the Federation Chamber, or attending committee or party meetings, undertaking research, preparing speeches, meeting constituents (people from their electorate) and dealing with matters on their behalf. They are still able to follow the proceedings of their chamber on televisions in their offices.
However, there is a quorum (minimum number of members present) required for both the House of Representatives and the Senate, and members and senators may need to return to their chamber to ensure this quorum. Members of Parliament are also usually required in their chamber for divisions (formal votes), during Question Time and, of course, when they are giving or directly responding to speeches.