Never Delete Images on the Day!
Post updated July 2021: Salvaging Images - When photographing weddings, I always take care not to delete all the images on the day. No matter how bad they look on the rear screen of my camera, I wait. Occasionally, you may be able to salvage something from them.
In the past when shooting portraits, I have had shots where the studio lights didn't go off meaning the shot was underexposed. However, during processing, a beautiful shot (click link to see before and after) emerged that earned me €800 as a large canvas print.
Similarly, at a recent wedding, I took a quick snapshot towards the end of the day. It was a shot that I would have normally deleted in the past but more recently, I have learned to keep these. At least until fully checking them out post-wedding.
I heavily cropped it and played around in Photoshop using some cool editing software and ended up with the image below. It isn't necessarily everyone's cup of tea but you never know, the little girl or her parents might like it : )
So, my advice is to not delete any images, unless seriously blurry, dark, irrecoverable or just plain rubbish, until you have had a chance to go through them during post processing.
You never know when salvaging images might pull out a corker.
P.s. This is also a reason why more megapixels is sometimes a good thing. For instance, take a 50mp image from modern DSLR's or mirrorless cameras. These photos can be heavily cropped into multiple, separate images that would all be good for printing or use in photobooks.