The Obama administration wanted to push its Iran deal through without bothering to ask the opinion of the Senate.
Senators didn't like it.
But politically, it’s important to show that Congress disapproves of the President’s diplomacy to such an extent that the Senate Foreign Relations Committee just advanced legislation 19-0 prohibiting him from touching Congressional sanctions until they review a deal. It builds pressure on the administration to explain what they’re doing. It will serve as a formal way for the Senate to have a debate on the floor. It forces the issue.
The Senate is there for a reason.
Not to look good during presidential speeches.
But to provide their input on the country's course.