No, not quite the same thing. Your Scrapbook bin is just another gallery. Only it's separate from your main gallery. There's a link to it from your gallery page. Images in scraps are still visible to those who have faved it. Images in storage are not.
You can put a pic in scraps by going to the deviation, clicking on Edit Deviation, and then selecting No Category. Images with No Category automatically get shunted to your scraps.
The best way to draw from imagination is to learn to draw from life or references first and really learn the object you're trying to draw from memory. I don't mean just know it in general. I mean really learn it in detail and also learn how the object behaves in different situations.
It's great that you already know how to draw from life. Next step is to know the object well enough that you can remember where all the details go without having it in front of you. And the step after that is to understand basics like lighting, composition, etc. well enough to be able to alter those remembered details to fit other situations with different angles, different lighting, different textures, etc.
For myself, I use references anytime I need to learn to draw something new that I can't figure out by logic or altering something else I already know how to draw. The more you reference, the easier it becomes to draw from the imagination for the future.
Your Scrapbook bin is just another gallery. Only it's separate from your main gallery. There's a link to it from your gallery page. Images in scraps are still visible to those who have faved it. Images in storage are not.