It would allow Greece to freely print money as it needs. Thus, trading "debt" for "inflation".
This is what Argentina did back in 2001. We had our money at a fixed rate of 1 USD = 1 Peso. The country could only have as many pesos as we had dollars in the central bank.
In 2002 we exited this scheme and made the Peso a floating currency. This allows the government to print as much money as they need to pay public employees and local suppliers.
Is it a good solution? Yes BUT temporarily. You can live with inflation for a few years if you do things right, and use that opportunity wisely. Create industry, lay off government workers, and basically allow things to take their course.
The problem is that Argentina has been abusing this for 12 years now. Instead of getting rid of government workers, they're taking more. They're also nationalizing railways and airlines (Aerolineas Argentinas operates at a loss of $1M a day). Instead of incentives for new jobs, they're giving away money to unemployed in "social plans".
Reading the comments about Greeks I'm guessing they will do exactly what we did: Exit the euro, devaluate, cover salaries by printing more money. Take the unemployed into government jobs. Forbid utilities from increasing their price (but giving them "subsidies"). In 3 or 4 years Greece will be a FINE place to live. You'll see a lot of expensive cars in the streets, lots of new buildings, overall support for the government. The president will be re-elected with an overwhelming majority. And in 10 to 15 years Greece will be struggling again. How do I know? Because as an Argentinian, this is what i live with every day.