Victory point cards are great to have because they create uncertainty in your opponents (is it a VP or a monopoly card?).
Obvious leads make you a target. Longest Road in particular should be picked up as late as possible. Joining up two separate road segments with a big road-building push and unveiling 2 victory point cards can give you the win from 6 points. Largest Army on the other hand needs to be more openly competed for, because of the play-only-one-development-card-per-turn rule. Victory point cards are great to have because they create uncertainty in your opponents (is it a VP or a monopoly card?).