When is it a good time to delete photos?

The header says it all really...I like my shots... I don't really want to get rid of them. Recently I moved a bunch of files from the main Lightroom catalog to a purpose built archive catalog for older shots that I wont be using anymore. These shots and the catalog file are on a separate hard disk offline to my main drives so wont be touched at all.

My other drives only have a finite amount of space so by using my workflow for getting rid of bad photos at the early stages, I do not have lots of left over shots clogging up the hard disk.

By comparison, I shot over 300 images for the Putney Bridge shoot last weekend. I whittled that down to the published 25 but still have over 200 liked shots sitting in a rejected folder. Some are very similar so using the Survey view mode I group those together and decide which of the liked shots are the best then ditch the others.

After that though, I am still left with full size DNG files which at the moment can be 18meg in size. There are options to use lossy .dng to cut down on the overall size or just keep them as .jpg files for posterity.

What do you guys do? Do you have infinite storage? Do you only keep a few from each shoot? Let me know in the comments.