Note that the IMF wants a reduction in debt-to-GDP ratios in the long run (commandment #3), even if nobody knows exactly what is the difference of having a 40% ratio, which they recommend for 'emerging markets' (meaning developing economies), or a 250%, as the UK had during the Napoleonic Wars (here). My first concern is with the idea that consolidation (by which they mean austerity) should be done by cutting spending and not increasing taxes (#4), because this is more conducive to growth.
This is a proposition they repeat in their last Fiscal Monitor (2012: p. 35), where we are told that:
"a number of earlier studies have shown that expenditure-based fiscal consolidations have a more favorable effect on output than revenue-based consolidations, in spite of the standard multiplier analysis … Chapter 3 of the October 2010 World Economic Outlook reaches the same conclusion (IMF, 2010b) and notes that this result is partly because, on average, central banks lower interest rates more in the case of expenditure-based consolidations (perhaps because they regard them as more long-lasting)."Note, however, that the reason for the superior performance for cutting spending instead of raising taxes (on the rich one would hope) is that the Central Bank does not hike rates in the former case, since it is part of a conservative plan to reduce the size of government (note that the IMF asks for consolidations to be fair, #6, but then wants to cuts social spending, #5). Worse the notion is also based on the idea that lower (higher) spending brings down (up) the rate of interest and leads to crowding in (out) of private investment. The problem is that the evidence for a positive (negative) effect of fiscal deficits (surplus), or public spending increase (reduction), on interest rates, is that it is almost non-existent (see UNCTAD, 2011, chapter 3 for a review).
The other point is related to the last commandment (#10), which says that you should coordinate your macroeconomic policies with other countries. I'm not even going to deal with the problems of coordination. My problem is that the arguments tend to be based on the Mundell-Fleming (MF) model (the ISLMBP with perfect capital mobility), which suggests that fiscal policy is less efficient in a small open economy. In this case, fiscal policy raises the rate of interest, with capital mobility, pressures for inflows lead to an appreciation of the currency, and lower trade surpluses. Instead of crowding out, meaning lower investment, one gets lower output from the external accounts. That's why they say in their last Fiscal Monitor that "in line with the theory, fiscal multipliers tend to be smaller in more open economies" (2012, p. 33).
Again this depends on a weak empirical relation. In the United States seldom is the case that expansionary fiscal policy causes higher rates of interest. In fact, the policy of the strong dollar, with the impact on manufacturing output and exports, has often been detached from fiscal expansionism or higher rates of interest (e.g. the Clinton years in which a strong dollar went hand in hand with fiscal consolidation and monetary easing to feed the dot-com bubble).
Finally, note that even small open economies in several periods were able to have very effective fiscal policies, because in spite of relatively flexible exchange rates, they used capital controls to avoid the effects of volatile capital flows on their external accounts. In this sense, the world of relatively regulated capital flows, rather than of fixed exchange rates (even if sometimes the two are confounded as a result of the Bretton Woods arrangement), seems to be more conducive to effective fiscal policy. So the lesson should not be that small open economies cannot do effective fiscal policy, but that capital controls (which they are not quite okay with contrary to what you might have heard, but I leave for another post) are necessary.
PS: For a more consistent theoretical critique of the MF model see Serrano and Summa (2012).