The vice president of the United States is the president of the Senate. In this capacity, the vice president acts as the presiding officer when present on the Senate floor. In the vice president's absence, a president pro tempore officiates Senate proceedings.
The president of the Senate, or any other presiding official, is bound by rigid rules of order developed by Thomas Jefferson to keep the executive branch from exerting too much power on legislative proceedings. The president of the Senate only speaks when ruling on points of order or reporting presidential electoral results. The only other role of the vice president as president of the Senate is casting tie-breaking votes. As a result, vice presidents mostly stick to their executive duties.