What's the practical meaningful difference between exercising your right to not vote, vs fulfilling your obligation to vote by showing up to the polling place a

What's the practical meaningful difference between exercising your right to not vote, vs fulfilling your obligation to vote by showing up to the polling place and drawing dicks on the ballot paper? Pretend you're an Australian and have a long tradition of fining people minor sums of money for not showing up. Why would you change to non-compulsory voting?