Main disadvantage: Iodine fumes are sensitive to different latent residues than other methods. It is possible that latent prints that would have been developed by iodine fumes will not be developed by other means, whose application will then destroy the residue needed for iodine development.
Advantage: Magnetic powders are designed to work on both porous surfaces and non-porous surfaces including plastics, Styrofoam, and rubber.