I use lightroom for my sports photos so the originals are always untouched on my harddrive. I delete anything that is no good, and certainly certainly keep everything that has been sent to agencies/publications in another folder as it was sent to them (ie cropped, resized, etc). Both my lightroom catalogue and that second agency export folder are backed up regularly onto an external harddrive, which itself has a mirror copy (that i update at home) - that way if im out shooting with my laptop and backup drive and loose all my kit i still have my catalogue on another drive at home.