From the Document: "The standing rules of the Senate promote deliberation by permitting Senators to debate at length and by precluding a simple majority from ending debate when they are prepared to vote to approve a bill. This right of extended debate permits filibusters that can be brought to an end if the Senate invokes cloture, usually by a vote of three-fifths of all Senators. Even then, consideration can typically continue under cloture for an additional 30 hours. The possibility of filibusters encourages the Senate to seek consensus whenever possible and to conduct business under the terms of unanimous consent agreements that limit the time available for debate and amending. Except when the Senate has invoked cloture or is considering appropriations, budget, and certain other measures, Senators also may propose floor amendments that are not germane to the subject or purpose of the bill being debated. This permits individual Senators to raise issues and potentially have the Senate vote on them, even if they have not been studied and evaluated by the relevant standing committees. These characteristics of Senate rules make the Senate's daily floor schedule potentially unpredictable unless all Senators agree by unanimous consent to accept limits on their right to debate and offer non-germane amendments to a bill. Also to promote predictability and order, Senators traditionally have agreed to give certain procedural privileges to the majority leader. The majority leader enjoys priority in being recognized to speak, and only the majority leader (or a Senator acting at his behest) is able to successfully propose what bills and resolutions the Senate should consider. Thus, the legislative process on the Senate floor reflects a balance between the rights guaranteed to Senators under the standing rules and the willingness of Senators to forego exercising some of these rights in order to expedite the conduct of business."
CRS Report for Congress, 96-548