Operations - Critical Path

The government spends a large amount of money each year on contracts. In fact, the federal procurement department spent over $425 billion in the fiscal year 2006 with over $33 million on Lockheed Martin Corporation alone. These projects are often known to have cost and schedule overruns.

Why would subcontractors for a government project want their activities on the critical path? Under what conditions would they try to avoid being on the critical path?