my main issue is the cost of changing national currency. we need a LOT of new banknotes, many documents need to be updated, people will make lots of mistakes early on, etc. etc. so imo we need to solve bigger issues like banking system and when all other big large scale problems are solved, we can slash those nasty zeros. this will take decades!
Honestly I think it makes it easier for people to do calculations and conversions. I for one always had to pause a moment before writing a check to convert Tomans to Rials. Slashing 4 zeroes makes it a lot easier for me. People always use Toman in Iran. So, you basically have to change billion to million and million to thousand.
So, 5 million tomans becomes 5 thousand tomans. Five stays the same, but for Rial, five had to change to fifty. Shifting by 3 digits is always easier than by one digit.
And issuing bank notes can take years to complete. We are printing money anyway for the reason I said before. As for rounding inflation, 10000 Rials is already so worthless that it won't make much of a difference. I highly doubt that this decision will make much of a difference to Iran's already high inflation.