In my country during the year 2016, 8th November the government announced currencies with highest denomination like 1000₹ and 500₹ won't be valued anymore. People are supposed to reach the banks and exchange it to any other denomination. In the event of this people suffered much, because there is no money to spend and banks were full of crowd. More than 100 lost their live standing in queue.
Whats the reason for such an immediate decision ?
The government stated it a reason to fight illegal funding to terrorism and recove the black money.
If there is validity or expiry for every currency same as day to day life needs, then people will make use of it and exchange to new currencies at the right time. This way everything can be made to be in circulation rather than getting accumulated for years. Here black money can also be avoided.
I first had to deal with this when I went to live in Hungary for a year. In my own country, it's a very rare thing for banknotes to have an expiry date. It's usually just that they stop making the banknotes of a certain type and every time you use one in a shop of other business, they don't give it back to you. So the collection of the banknotes doesn't fall on regular people, it falls of businesses, I guess. But withing my year in Hungary there were a couple of banknotes that were close to their expiry date! I used those I had in the shops prior to the date, but I still had to go with a friend of mine to a bank one time when she had an old banknote.
It's good that with cryptocurrencies it's not an issue at all because it's impossible to make counterfeit crypto due to the nature of how blockchain works.