As a new astrophotographer I found this video explaining eyepiece projection very helpful:

The video:

1. Solved the mystery of why planets appeared on my camera screen simply as bright dots.
2. Showed me how to get much more detail in my planetary photos by using my eyepieces and image stacking.
3. Explained when and where eyepiece projection can be useful (small, bright objects) vs. prime focus (large deep space objects).