Encontrei uma postagem de um funcionário da Dell no fórum de suporte da Dell isso explica muito bem:
Dell Inspiron n5520 comes with multiple video cards. You will not be able to know which GPU is active using the ‘Catalyst Control Center’. This feature has not been provided by AMD.
In Muxless hardware design, the switchable graphics will use appropriate video card to assigned application from the catalyst control center and process the graphics of the application and give the output through the Intel’s integrated video card so using any application on windows you will not be able to see the discrete video card.
Therefore, when you are using graphic intense programs, (Example: Playing games, video editing, photo editing) the discrete graphic card turns active.
However, during normal usage, if you are viewing applications like office, power point or word documents the integrated graphic card turns active.
O mesmo post continua explicando que você tem algum controle sobre isso através do software usual ATI / AMD Catalyst Control Center. Também oferece algumas soluções para situações em que as opções podem não aparecer no CCC.