The incomplete file is what has been d/loaded so far. If you delete it, you are deleting the file and it'll have to be started over again. When you preview a file with LW, it leaves a copy of the preview in the incomplete file in the library. It'll be in red have a long number before the title. You can saftely delete them.

I'm curious, if you don't have room for the incomplete file, how can you expect to have room for the completed file?

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