You might want to do it for the benefit of the author. If you see a nice post by an unknown author and feel you want to give up your award for so that the author gets more (and also the post has a bigger chance to be noticed) - then you vote early. So it's a kind of altruistic action.
But please note that this process is not black-and-white, e.g. if you vote 15 minutes after the creation you achieve an outcome which is something between voting after 0 minutes and voting after 30 minutes. You would need to refer to the official documentation for the exact algorithm that controls the curation reward.
perfect, thanks for the reply, much appreciated