3D CAD links (of piping, for example) appear in sections as if viewed from an infinite distance away (instead of just cutting through the elements at the section's cut plane). The current workaround is to link the CAD file into an in-place Generic Model. This is silly. If Revit knows how to "cut" the 3D CAD geometry when it's in a Generic Model family (which IS a cuttable category), why can't it do so when linking it in directly? This would also avoid the issue with Shared Coordinates not being respected when linking into In-Place families.
This is also related to the idea to have an option to make all families cuttable regardless of category: Cuttable vs Non-cuttable Families
EDIT: And somewhat related to linking civil 3d pipe networks into revit