incomplete files and download/saving process

Limewire is my fav P2P file sharing program but it crashed my computer and I had to go into windows safemode command prompt to delete in-use incomplete files and unsaved files. I got out of low diskspace hell but it was a pain.

Basically why are files downloaded into a separate "incomplete" file folder and then copied over to the destination folder after download completion. The problem with this is that you actually need more HD space just to download a file. A 700mb file actually requires 1400mb collective HD space or so to download and then is copied over (not moved) to the destination folder and then the file is deleted from the "incomplete" folder if this process is completed successfully. Why not just have the downloaded files managed in the destination folder and get rid of the "incomplete" folder all together. Could just have partials located in the destination folder (with whatever cryptic weird filename) and once download is complete, just rename the file to the correct filename. It just doesn't make any sense to me to have 2 copies of a file at any given time during the download/save process. Any thoughts?