Deleting imported movies in "imported" folder

Dear all,
I noticed that there is a huge amount of data in various “imported” folders. I always thought cs creates only symbolic links, but I have raw data in these folders. Is it save to delete them directly?
I see that the imported files have a 21 digit prefix. If I need to run a job that needs these files, like motioncorr, could I simply restart the import job? Or are these prefixes necessary to keep?
Best
Dario