If you buy a Haynes manual, most of the procedures are illustrated by photos taken while the writers have been working on the car. Magazine articles are illustrated in a similar way, I know, I've taken the pictures.
However I often find that with the advent of digital cameras I take photos just for my own reference. Such a photo is shown here. For those who don't recognise it, it's the inside of a ceiling rose. Dangling at the end of the white cable in the middle is a light bulb and shade.
This rose was playing up and needed to be replaced. I took the photo so I could remember where all the wires went once I'd screwed the new rose in place. Good job I did too as I probably wouldn't have remembered the grey wire on the left which runs to the switch needed to go with the live wire to the light. Then there would have been some head scratching and hopefully a lucky guess.
Very handy if you have a rubbish memory or just worry about putting things back together. Best of all, with digital you can shoot away (a compact is good for this) and then delete the photos once you've finished the job. It's like a notepad but quicker.