An inline fan does not rest directly on the ceiling of the bathroom.  Rather - the fan installs in the attic space above or slightly away from the bathroom. 

Advantages over a traditional bathroom fan: 

SOUND - because the fan is mounted 6' or more away from exhaust point on the ceiling - fan vibration and noise is eliminated.  The insulated ductwork used in an attic protects it from condensation and provides an excellent sound dampener.

MULTIPLE EXHAUST POINTS - in a larger bathroom, it is possible to create mutiple exhaust points in the ceiling and only install 1 fan.  This is done with a WYE connector, some flexible ductwork, and multiple grilles.  Grilles are available in many shapes and sizes, and can also be purchased with lights.