Hi,
What are you trying to achieve?
The geometry object (Point, Polygon, etc.) classes and the GeometryEngine class allow you to work with latitude and longitude coordinates, or geometries in other units, as geometry objects aren't bound to a particular spatial reference - it depends what the spatial reference of the map/layer they are being added to is. For example GeometryEngine has a project method which takes a longitude, latitude, and output spatial reference, returning a point in the units of the output spatial reference, for dealing with geometries which have been defined using latitude longitude coordinates.
~elise