In order to give your readers, viewers or listeners a reason to support you, you should aim for milestones. A goal is such a (financial) milestone.
You may simply want to generate regular income from your content on a permanent basis, live from what you like to do well. For a marketing campaign, however, it is often abstract. Break down your big goal into individual projects, linked to a certain amount of money. Explain what you intend to do first: if you reach 500 Euros or Dollars you would be able to publish one post or one video per month. The next goal could be: publishing a photo gallery or a podcast, once 1,000 Euros or Dollars have been reached.
Goals you make your work transparent and your campaign more urgent. Potential members often want to know what you need money for. Setting goals is effective in turning audiences into members. Find example goals here