Experience in other countries shows that circa 15% of the money "floats" in the recipient country and is used to finance consumption. This should translate to 1 billion free floating dollars in the hands of the 2 million citizens of Macedonia. Billions are transferred to the outside world (mostly to finance additional transactions, some of it to be saved in foreign banks away from the long hand of the state). A trickle of money comes back and is "laundered" through the opening of small legal businesses.
These are excellent news for Macedonia. It means that when the macro-economic, geopolitical and (especially) the micro-economic climates will change - billions of USD will flow back to Macedonia. People will bring their money back to open businesses, to support family members and just to consume it. It all depends on the mood and on the atmosphere and on how much these people feel that they can rely on the political stability and rational management. Such enormous flows of capital happened before: in Argentina after the Generals and their corrupt regime were ousted by civilians, in Israel when the peace process started and in Mexico following the signature of NAFTA, to mention but three cases. These reserves can be lured back and transform the economy.
But the black economy has many more important functions.
The black economy is a cash economy. It is liquid and fast. It increases the velocity of money. It injects much needed foreign exchange to the economy and inadvertently increases the effective money supply and the resulting money aggregates. In this sense, it defies the dictates of "we know better" institutions such as the IMF.
It fosters economic activity and employs people. It encourages labour mobility and international trade. Black economy, in short, is very positive. With the exception of illegal activities, it does everything that the official economy does - and, usually, more efficiently.
So, what is morally wrong with the black economy? The answer, in brief: it is exploitative. Other parts of the economy, which are not hidden (though would have liked to be), are penalized for their visibility. They pay taxes.
Workers in a factory owned by the state or in the government service cannot avoid paying taxes. The money that the state collects from them is invested, for instance, in infrastructure (roads, phones, electricity) or used to pay for public services (education, defence, policing). The operators of the black economy enjoy these services without paying for them, without bearing the costs and worse: while others bear the costs. These encourages them, in theory to use these resources less efficiently.