There's also the risk of a redenomination. Bank accounts and other monetary instruments are automatically converted in that case; physical cash has to be brought to a bank to be exchanged, and there's often a time limit.

And there's also the risk that, as newer notes and coins come with stronger anti-counterfeiting measures, older notes and coins aren't accepted anymore, or accepted only with a discount over their nominal value. (I've seen it happen with older USA dollar bills left over from a trip to the USA a couple of decades before.)