Metal sheet here means thin flat stock in lead, brass and other metals, soft enough to be cut with shears and formed between your fingers. On a model it becomes plate patches and covers, folded edge trims, improvised armour, and ballast hidden inside a fuselage to stop the model sitting back on its tail.
The advantage over plastic is simple: metal keeps the fold exactly where you put it, with no spring-back and no whitening along the crease.
Very thin sheet is cut with shears, and the edge then has to be dressed with a file, because a sheared edge is left sharp and slightly rippled. Fix it to the model with cyanoacrylate on a degreased surface; solvent modelling cement has nothing to key into on metal. Strip, rivet strip and self-adhesive metallic foils are in the brass strip, perforated sheet is under mesh, and sections are in the metal profiles.
