FTP allows sending across networks that can be located anywhere on the Internet. FTP does not posses storage management capabilities which means if not manged properly, FTP shares, once filled up, will stop receiving files from the camera. Accessing files that were sent using FTP requires an FTP client or the internal NAS file manager. Other retrieval options include dedicated Windows or Linux FTP servers that have custom file access built around them.
Since in most cases FTP is going over the Internet, it has to be more robust against outages. Cameras that are equipped with an SD card will store all files in case of a network outage until the outage is over. At this point, the camera will forward the stored media to the remote FTP server (store and forward).