By Mohamed El-Erian, Bloomberg View

The net overall impact of this year’s 28% plunge in oil prices is positive for the global economy. But it isn’t universal, and it comes with negative dimensions that need to be well understood, lest they end up reversing the benefits.

The good comes from the boost that lower oil prices provide to consumers and manufacturers in oil-importing economies. It is the equivalent of a significant tax cut at an opportune time, especially for Western consumers. And while part of this benefit may go to governments because of the way oil taxes are imposed in certain countries, particularly in Europe, the overall global effect will be to boost consumption and lower manufacturing costs in countries that have been struggling to overcome prolonged malaise in growth and jobs.

There is also a positive distributional effect within these economies, although it is marginal rather than decisive. Because energy spending constitutes a bigger part of the budget for lower-income families, lower oil prices help counter some forces that have worsened the inequality of income, wealth and opportunities.

Yet it would be foolish to ignore the risks of lower oil prices. For one thing, they lead to immediate cuts in energy companies’ investment budgets, both in the traditional sector and among promising alternative technologies. As a result, longer- term energy potential will be undermined, both overall and in its more environmentally friendly components.

In addition, the lower oil prices, which would normally be seen as producing “good” disinflation in oil-importing countries, could accentuate the general deflationary tendency in Europe—one that could be quite detrimental to the continent’s immediate and longer-term economic well-being. While I believe the favorable income effects help offset this threat, it would be wrong to ignore it given that Europe is already in uncharted economic terrain.

A third risk relates to certain segments of the financial markets. Look for the plunge in oil prices to be disruptive for the commodities markets as a whole, and for securities issued by energy companies and oil-exporting countries. Given the weight of investments in these securities in certain emerging-market and high-yield indexes, the result could mean generalized pressure to sell in these asset classes.

Besides these three bad outcomes, there is also the ugly: The possible reaction of certain oil-producing countries that are particularly hard hit by the price declines. Nowhere could this prove more consequential than in Russia.

Roiled by sanctions, a collapsing currency and large capital flight, Russia now faces the effects of a sharp fall in oil revenue. Companies pushed to the brink may be looking for government support at a time when the authorities’ ability to respond is curtailed by the decrease in their own revenues. The effect will be to strengthen the winds of recession, inflation and financial instability in Russia.

How this affects the global economy depends in great part on Russian President Vladimir Putin. Up to now, Putin has been able to resort to regional geopolitical adventures, most notably in Ukraine, to counter and divert popular dissatisfaction in Russia over the domestic economy. And he has done so notwithstanding the resulting imposition of Western sanctions on his country.

Will the additional domestic downturn lead Putin to change course on Ukraine as a way of lifting Western sanctions and alleviating overall pressures on the economy? Or will the internal pressure push him to extend his regional adventures?

Should Putin take the second course, the West may impose more economic sanctions, including on the energy and financial sectors, and Russia would probably follow with counter-sanctions on energy supplies to Europe. This could push Europe into recession—which would negate much of the good impact that lower oil prices have had on the global economy.