"Saved states" can be one cause. A copy of each state needs to be retained in history for "undoing" if need be.
With large files, that can take up a lot of space.
That's why it's recommended to use an external or second internal HD for a "scratch disk". You want to have a good chunk of free space if working with complex or large files.
If you're working with small files and it's taking that kind of space, there may be something else you need to look at.