Not necessary in actual democracies where you have 10+ different parties.
There, abstaining is just an other party. One with a powerful voice telling the politicians that if enough people not vote, it is a big sign that something is wrong with the system and things will need to change to prevent riots.
It is not the same as voting blank, which is also possible. Then your vote gets added to the most popular vote. In a way of saying that you are content with any.