Since Greece accepted the new bailout they will have to cut government employment, and employee salaries. And since a large number of Greeks are government employees, the result will be less spending. Less spending leads to a weaker economy.
If they choose to o back to their old currency, the drachma, their currency would be weak. A weak currency would lead to less spending, which leads to a weaker economy.
It's almost laughable, either way they would be, well you know. I feel sorry for the politicians right now.