Use By Papal Conclave
Before the opening of the conclave the Sacred College assembles in this chapel to attend a sermon in which the members are reminded of their obligation quickly to give to the Church her ablest son as ruler and guide. The cardinals then withdraw to the Sistine Chapel. In the Cappella Paolina are sung daily the conclave Solemn Masses "De Spiritu Sancto", at which all members of the conclave must be present.
In 1549 and 1550, the Cappella Paolina was used for the papal conclave itself, the Sistine Chapel having been set aside and divided into 19 cells for use by infirm cardinals. The conclave elected Pope Julius III.
Read more about this topic: Cappella Paolina