You get a second chance to refine your photos
There is a high chance you may not have judged the exposure triangle properly. It happens to me every time because photos are spontaneous, and it can happen anywhere. Here comes editing into play. Maybe you have overexposed it by 2 stops, or maybe 1 or 2 stops under, or maybe you have messed up the white balance. You can easily fix it with editing and make the photo usable. There is also a high chance that photo might be a great photo, and you don’t have any other version of it.
It helps you establish your own style
If you see the works of legendary photographers, you will notice they have a very unique way of composing their photos, and they also have a very unique colour palette in their work. Composition is a different topic, but the colour treatment is part of their post-processing. They simply try to make the look similar across their work so that even if there is no logo or anything to identify who took the photo, you will still know the photo is by that photographer.
So now the question is, how could you know who has taken the shot? Yes, it is because of their composition, and moreover, their colour profile. If you see a photo by Alex Webb or Cartier-Bresson, you will definitely identify that the photo is by them.
Over the years of editing experience, you will develop your own style of processing, and that will end up being your own signature style.