Commodity money has two sources of demand (the commodity usage and for a medium of exchange) which helps stabilize it against crashes. It reduces people’s fear of being stuck holding the bag at the end when no one wants it anymore (this comes up in e.g. major inflations or crashes with government fiat moneys – no one wants to have the money last when it no longer has value, which drives the value down in advance when people predict the currency may die). With e.g. gold, you may be left with something that has lower value than it used to, but it will still have value (and it’d be hard to guess in advance what else would hold its value better, taking into account storage downsides – even with the reduced value it’d still be a reasonable thing to have, which is one of the reasons it will retain value as a medium of exchange even in bad circumstances).