Cuttable vs Non-cuttable families

You want to know which families are cuttable and which are not. Revit 2011 help gives the answer:

Cuttable families (link):
Casework
Ceilings
Columns
Curtain Wall Panels
Doors
Floors
Generic Models
Roofs
Site
Structural Columns
Structural Foundations
Structural Framing
Topography
Walls
Windows

Non-cuttable families (link):
Balusters
Detail Items
Electrical Equipment
Electrical Fixtures
Entourage
Furniture
Furniture Systems
Lighting Fixtures
Mechanical Equipment
Parking
Planting
Plumbing Fixtures
Specialty Equipment

What is a cuttable family?

If a family is cuttable, the family displays as cut when the cut plane of a view intersects that family in all types of views. From Revit 2011 help.