Hi @ruralwannabe, thanks for bringing this to our attention.
As it sounds like you enabled the computer backup feature, certain folders you selected would have moved into the Dropbox folder.
If your Dropbox account runs out of space, nothing will happen to the files on the local computer. However, any changes won't sync to the Dropbox site until it has enough quota to add files.
Regarding the Recent Files folder, could you clarify if this is on the Dropbox site or the local machine?
This will help me to assist further!