Although I use a cloud backup for images*, I also have them locally just because it seems faster to loop through them whenever I need - and for most of the cases that would be creating a selection of photos for printing out, posting online, whatever. And that is acknowledged to be one of the most tedious task humanity ever met.
* after I lost a considerable amount of photos back in 2003
My first attempt to solve this problem was image-categorizer, which works. But it was memory-consuming (Java is not exactly great for image manipulation) and it required to be used in the same computer where the images are. That was really annoying when someone else was helping me to pick the photos. So selektion was born seeking for mobility and performance.