The framers of the U.S. government borrowed many elements of British parliamentary practice. One was the Committee of the Whole, an institution originating in the House of Commons, and then used in colonial legislatures, the Continental Congresses, and the Constitutional Convention. As you might see on CSPAN, the modern Committee of the Whole is a way to organize the House under different rules to expedite the consideration of complex legislation, often appropriations bills that are subject to multiple amendments.
The Committee of the Whole varies from normal House practice in several ways. The Mace is lowered from the top pedestal on the Speaker's right to the lower one. The requirement for a quorum drops from a majority of Members to 100. In many cases, Members are better able to offer amendments to legislation and gain access to the House Floor to speak on their behalf. And the Speaker leaves the presiding officer's chair and a "chairman" of the committee takes over with marginally reduced responsibilities to maintain order.
This last detail is particularly important because of its origins. The Committee of the Whole developed early in British parliamentary practice as a way to get the Speaker out of the chamber. The Speaker served as presiding officer and representative of the Commons to the king but also as the king's representative in the Commons. This duality created conflicts when parliament wanted to debate something the king may not have liked. The speaker essentially acted as the king's spy. In his book on parliamentary procedure, Speaker Thomas Brackett Reed of Maine wrote that the Committee of the Whole enabled the Commons to deliberate and speak "their real sentiments" on issues of taxation and appropriations, in particular, without their speaker in the chair threatening to relay their frank discussions to a sovereign who could kill them.
Being in parliament during the Middle Ages, when the Committee of the Whole developed, could be dangerous work. Eight speakers of the House of Commons were beheaded or murdered between 1399 and 1535. Many more regular members of the Commons were executed or imprisoned in the Tower of London. Free speech, particularly during parliamentary sessions, was not guaranteed. Amid this uncertainty, practices evolved to protect representatives in the Commons in their work. These practices, like the Committee of the Whole—forged after years of brute force, intrigue, and drama—continue to inform how the House of Representatives does its work today . . . though with considerably less violent results.
Sources: Thomas B. Reed, Reed's Rules: A Manual of General Parliamentary Law with Suggestions for Special Rules (Chicago: Rand, McNally & Company, 1898); John Sullivan, House Practice: A Guide to the Rules, Precedents, and Procedures of the House (Washington: Government Printing Office, 2011).