The history is a great concept but it is not always simple to use. Many operations requires multiple images and you must be sure that all referenced images and files are present when you apply an history.
To my knowledge, saving the project is the only safe automatic way to ensure that you have the required environemt to continue processing your image later, including using the history.
Alternatively you may move the image you process AND ALL REQUIRED IMAGES OF THE HISTORY (like masks) to a workspace, and save only that workspace. Maybe an automatic way to select all images referenced by an history recursively would be useful - but this is a topic for the wish list.
If you just want to refer to the history, you can save it as a process icon (move it from the 'history' view to an icon, then save the icon). It may or may not be useful without the referenced files/images.
-- bitli
