Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

When entering a Futures contract, must the margin deposit be idle or can I profit from it?
In theory, an FCM may accept various types of collateral, including assets such as cash, treasuries, certain stocks, sovereign debt, letters of credit, and (as of 2009, I think,) gold. In practice, most will want you to post cash or cash. Some will take treasuries, but I think you'll generally have a hard time posting securities or other riskier asset classes at most shops, as dealing with the margining around them is more complex (and less profitible).