Too many retarded people with aids in this thread to actually answer your question.

The correct answer is as follows: Spoiled ballots are counted while none voting isn't. The reason this is important is because political parties care about votes, and why you aren't voting for them. Imagine if in every seat, 6% of current labor voters voted Green instead. This is going to translate into seats lost for Labor, causing them to investigate why, and whether it's worthwhile moving closer towards the green's point of view.

Spoiled ballots are similar to this, in which you are voting for "none of the above". Ignore the retarded whore fuckers in this thread suggesting that no stats are gathered from these votes: In reality the vast majority of spoiled ballots are purposefully done: The political system knows this, and the "too dumb to vote" are a minority that can be ignored by everyone, there is a reason these stats are counted.

Now the main difference between not voting all, and spoiling your ballot, is not voting at all suggests you don't give a shit. To put it frankly, to politicians your opinion isn't important because you don't believe it important enough to take the time out of your day to go vote. Chasing after someone who doesn't care is a waste of time. On the other hand, spoiling your ballot tells politicians that your vote is up for grabs if they manage to attract you.

Currently, the numbers of spoiled ballots is around 1%, so enough for certain parties to care slightly, but not enough for major change. If a higher number is voted, it creates a new generation of voters that can be fought over. A good example of what happens regarding this is the SNP.