Due to the dynamic nature of the files directory it is not a good idea to link direct to files with /sites/default/files/etc paths.

If you configure Linkit for file entities so that URL type is 'URL type' or 'Download file link' then you are going to end up with those direct file paths in your content, which may later break.

It would be good to raise a notice about this setting if it is configured in a potentially risky way.