These settings control Arnold's tessellation of subdivision surfaces. Note that, as well as the global subdivision control described below, you can also control the subdivision of an individual object, via the Arnold settings on the Attribute Editor. Select the geometry object in question in Maya, go to the Attribute Editor, scroll down and expand the Arnold group, and choose a suitable value for 'Subdivision Iterations' (there are also other controls for per-object subdivision. The actual number of subdivisions for each object will be the lower of the two values.
This value sets an upper limit on the number of subdivision iterations for all objects. By default, this is set to a very high value (999) which in practice has no effect. Setting this to a low value such as 1 or 2 can be useful when debugging scenes that take a long time to subdivide/tessellate.
Dicing Camera menu found under Subdivision in Arnold Renderer tab of Render Settings