My big problem with importing into lightroom then deleting, is that it is very hard to quickly go through pictures. It takes time to load each picture, then when you press delete, you wait half a second before the confirm button comes up, then deleting takes half a second. With Fast Picture Viewer, it takes literally a quarter of a second for the entire process.
I can delete bad pictures in a tenth of the time from the card itself when compared to Lightroom.


