Gold and silver have traditionally been used for decoration as in jewelry, and as money, later to back paper currency. They all have commercial uses: gold in dentistry and electronics, silver in photography, platinum, palladium, and rhodium in catalysts for processing petroleum or chemicals, and in catalytic converters for automobiles.
Some regard investments in precious metals as a hedge against inflation. These metals are highly valued and can contain large amounts in a small space. That makes it possible to conceal and/or transport considerable value. However, they are heavy. Protection from theft poses special issues.
Some regard precious metals as a special class of commodities. They do trade in world markets.