If you save a draft and want to access it later, you can just select the draft from the new ‘Drafts’ panel that appears above your image library when starting a new post. For people who like to be ahead of the game, but don’t want to pay for scheduling apps, this could be a way to get several posts started and ready to go, all ready to post when you have time to jump in and press post.
There are, however, two pretty big caveats to the new feature. The first, you will not be able to save a draft unless you have made edits to an image, tagged someone, or written some sort of caption. In the grand scheme of things, this is not so bad. But the second caveat is that once you save the draft you will be unable to make any more visual edits to the image, meaning all you will be able to change is your tags, caption, etc.
Caveats aside, this is a welcome addition in my estimation. If you would like to take advantage of it you can download the latest Instagram update now.