On the bulletin board above my desk, I keep a handful of quotes that have taught me something, or that I hope to learn from.
The best time to share your work is when you can't figure out how to make it better anymore.
This one comes from an episode of Koppelman's podcast, The Moment, but damned if I can remember which episode.
I largely agree with this one. But depending on your audience and the circumstance, there may also be a risk. For instance, if you've sold a project before you've made it, the person who bought it has already imagined what it will look like. When you finally share your work—particularly if you've learned things about the project in the making of it—the potential for disconnect may be high.