The Economist has some incisive answers.

If Mittal acquires Arcelor it may be well placed to bargain with customers and suppliers and thus ride out any slump. Three suppliers dominate the global market for iron ore and coking coal. In 2005 they raised prices sharply. Further smaller increases are likely this year. Scale will confer on Mittal more power to resist price hikes. Furthermore, a combination of the mining activities of Arcelor and Mittal will foster self-sufficiency. Mittal claims that the new firm will expand its iron ore operations to provide half of its own supplies by 2010.