Difference between LR download backups and backups??

Sorry if this question is already answered, I couldn't find it. My hard drive is full. I have realised that I can delete some of the LR catalog backups by doing this from the folder titled "backups" however there is also a huge amount of data being used in a folder called "download backups" it seems to be full of actual photo files. This is not, as far as I'm aware, a duplicate back up system I have set up. For one thing it only includes some of my imports. I suspect that I have done something in settings during importing that created this. Can I delete the files without causing havoc? any help would be much appreciated.