Thus, the legislative procedures on the Senate floor reflect a balance—and sometimes an uneasy balance—between the operation of its rules and the principles they embody, on the one hand, and pragmatic arrangements to expedite the conduct of business, on the other. In addition, by custom, only the majority leader (or another Senator acting at his behest) typically makes motions or requests affecting when the Senate will meet and what legislation it will consider. In fact, there are few Senate rules that limit the right to debate, and no rules that permit a simple majority of the Senate to end a debate whenever it is ready to vote for a bill, amendment, or most other questions being considered. Filibusters and Cloture

The dearth of debate limitations in Senate rules creates the possibility of filibusters. Even the additional 30 hours allowed on a bill under cloture is quite a long time for the Senate to devote to any one bill, especially since Senators may not be willing to invoke cloture until the bill already has been debated at considerable length. Furthermore, all Senators have legislation they want to promote. When a Senate standing committee reports a bill back to the Senate for floor debate and passage, the bill is placed on the Senate's Calendar of Business (under the heading of "General Orders"). To avoid this possibility, the majority leader attempts to get all Senators to agree by unanimous consent to take up the bill he wishes to have debated. Unanimous Consent Agreements

		The Nature of Unanimous Consent Agreements

Just as the right of extended debate encourages Senate committee and party leaders to bring up bills for consideration by unanimous consent, the right to debate combined with the right to offer non-germane amendments encourages the same leaders to seek unanimous consent agreements limiting or foreclosing the exercise of these rights while a bill is being considered. Ordered further , That upon the use of yielding back of time, the Senate vote in relation to the amendments in the order listed; provided, that no second degree amendments be in order to any of the amendments prior to the votes; provided, that no motions to commit be in order; provided further, that upon disposition of the Toomey amendment, the bill, as amended, if amended, be read a third time and the Senate vote on passage of the bill, as amended, if amended; further, that the vote on each amendment and the vote on passage of the bill be subject to a 60 affirmative vote threshold; provided further, that the Secretary be authorized to make technical changes to amendments if necessary to allow for proper page and line number alignment. Senators also may agree to time limits on individual amendments before offering them.
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.