Consider your original digital files as you negatives/slides. The derivatives then can be considered as prints.
So, the originals are the (untouched) source and the derivatives the (edited) results like black/white, panorama, HDR, retouch and colorimprovements.
But, with modern applications like Lightroom you can make 'derivatives' without making (working) copies from an (untouched) original. The changes in these PIE applications will only reside in the database, not affecting the original RAW data. So, i.e. you can make a black/white image without removing the color information. These loss-less changes are called PIE (http://www.dpbestflow.org/image-editing/parametric-image-editing
When every change can be made in PIE ware, there will be less need for 'real' derivatives in the future. Then you have only to take care of your originals + the PIE ware database (were all the derivatives resides).
Hope this is helping you?