You preview a lot of files. Do you make sure you delete the preview files out of the incomplete folder? These files are called PREVIEW-xxx.avi, etc. They can take up considerable space. So deleting these will free up space. Probably worth defragmenting your Hard Disk Drive after doing this. A fragmented HDD or/& one that's running short of space can slow the system down.

You 'might' also consider this: Tip: Purge the Downloads Queue!