Question

In addition to replacing the president if necessary it's the duty of the Vice President to

Answer 1

review laws before the president signs them.

Answer 2

Veep is president of the Senate and casts a deciding vote if there is a tie in the Senate.
He had better at least bring the Electoral College votes of his own state on Election Day.
Other than that. He hangs around being useless unless the President needs somebody to go to a B list funeral.