In response to post #49982472. I think what he meant it's, when you download a mod with NMM, the zip file is stored in the "mods" folder of NMM, when you install it, it decompresses the file into a folder and creates the symlinks, but the original zip file is still in the "mods" folder. At this point, a mod is actually using twice the space needed (zip file + decompressed folder, really noticeable in large mods like SMIM or texture mods that can reach easily a GB or more). In MO you could delete the downloaded zip file to save space and the content of the mod would still be installed, but in NMM, if you delete the downloaded zip file, NMM removes the mod completely.