If you list out the things someone wants from a currency Euros are better in every possible way than the local made up currency we are talking about here. More widely accepted, more usable to pay official debts, more difficult to counterfeit, more controlled in their supply, more likely to retain their value, etc.
Ok, let's put it another way.
You want to buy a bike, that costs 200 euors. People generally take the bike now and pay at the end of the month. Next week, Greece drops out of the Euro, and everyone's pay is converted from euros to NewDrachma, which has an initial peg of one euro to the NewDrachma. Unsurprisingly, it's actually worth a lot less. You're now paid in NewDrachmas, but to get the euros you owe, you'll need to pay far more New Drachmas than you earn. Because of this risk, you're reluctant to buy the bike, and the seller is reluctant to sell you one.
So you could agree to do the deal in NewDrachamas. Except that you don't know if there will be a NewDrachama, or if you'll be on Euros or casino chips or whatever.
If you make up your own currency, however, then you can fix it as much as you like. Bikes cost 200 dismos. Shoes cost 50. You'll be able to get 4 pairs of shoes for the sale price of a bike, no matter what the politicians say. If you know the people you do business with, and you trust them to be around in a month's time, and you're likely to be buying stuff from eachother for the forseeable future, then this is a sensible enforceable contract that doesn't load one side or another with potential fx risk if there is a sudden change in the currency system.