Before the days of digital photography, the film was processed in a series of chemicals and that was it. The process would take about an hour, but usually it would be sent to a specialist laboratory to be processed and the turnaround was around two days, sometimes longer.
With digital cameras, the processing is done on a computer. This means importing the images into professional editing software.
I use Adobe Lightroom. Each picture is approximately 25mb in size, so it does consume hard drives very quickly! Once they are in Lightroom, they have to be checked, with a number being rejected for various reasons. Once the final selection has been identified, each picture has to be 'brought to life' with the skills of the photographer using the software.
On average I would take around 6 hours to complete the processing of a wedding I have photographed.
Often during wedding photography, there are difficult lighting conditions and you don't have the time to create elaborate lighting set ups. Using additional light at the from in this example would have made the picture look very false. So just thinking ahead of what the result could be after processing, allowed me to take this in natural light to get a much more pleasing picture.