Why should the Senate defer to the president's choice of who he wants working under him?

There are reasons why the Senate should defer to the choices the President makes regarding whom he wants to work with him. It is important for the President to be able to choose people with whom he will be comfortable working. These people will help the President carry out his vision, and they should be people who are generally supportive of the President and his ideas and goals. It is important, for example, that the President and the Secretary of State share the same goals for American foreign policy. The Senate should not be an obstruction to the President; by not allowing the President to choose a Secretary of State with whom he is comfortable, the Senate potentially impedes efficacy of the executive branch.
It is also customary for the Senate to give the President an opportunity to implement some of his ideas and policies. To do this, he will need people who share his vision, ideas, and goals. Finally, when the President is successful in accomplishing goals that are beneficial for the country, the country benefits. The Senate should be supportive in allowing the President an opportunity to accomplish his goals that benefit the country. One way to assist with this is to have people in place with whom the President feels comfortable.