President and Vice President have to be elected together.
The nearly disastrous election of 1800 caused amending of the Constitution which led to the 12th Amendment being created. Before the Amendment the Constitution called for a President from one party and the VP from the other. In 1800 two candidates from the same party got an equal amount of votes.
Passed June 15, 1804
Why is it still important?
Today if the President and Vice President were from different parties they would have complete opposite views on different topics. Like how the Democrats are for abortion and the Republicans are against abortion.