Why does SimpleScan scan to memory?

I recently started using SimpleScan for scanning larger documents, which works great.

However, I noticed that after around 70 pages my computer started slowing down considerably to the point of freezing. After leaving it for a few minutes, it slowly came back to life and I decided to check what program was keeping my computer busy so much. I was surprised to see that SimpleScan took 60% of my computers 2GB of RAM. I scanned another page and noted that the memory use increased to 61%.

From this I concluded that SimpleScan must scan to memory, instead of to disk. While I can imagine this is a good idea for scanning a few pages, for an application of which the interface seems to be geared towards scanning bigger documents, I find this a rather peculiar choice.

As I don't really think it is a bug in the normal sense, I decided to make this into a question.
My question therefore is: why is SimpleScan scanning to memory instead of to disk? Scanning to disk would have quite a few advantages, such as restoration of session in case of crashes.

thanks in advance!

Edit: in addition to restoration of session, it would also become possible to have multiple documents open at the same time.