With good cameras you can use different lenses, e.g. a wide-angle lens, when
Many cameras have a portrait setting to use when
You zoom in when
A photo can be blurred if
A photo can be out of focus if
You enlarge a photo when
You use flash when
you are far away from something and you want to take a close-up of it.
you want to take a photo of a person.
you want to make it bigger.
you move when you're taking it.
your camera isn't automatic and you haven't used the right settings.
you can't step far away from your subject but you want to get all of it in the picture.
you want to take a photosomewhere dark, e.g. indoors or at night.