Many people feel that their privacy is being invaded when location services is used in iOS, but many photo apps can't be used to their full potential without enabling location services on your iOS device, and within specific apps.
Why do so many photography-related apps on iOS require that location services be enabled?
Why is the photo editing app you just downloaded telling you it wants to use your current location?
When you take photos with your iOS device, most smartphones, and many modern cameras, location information can be stored in the metadata of the file. This process of storing GPS coordinates in photos is referred to as 'geotagging' and reveals the location where the photo was taken. The GPS coordinates stored in photos allows anyone with access to this data to precisely plot on a map the very spot where the photo was taken, often down to a specific address. While some people want this information stored with their photos, many see it as revealing too much. More likely than not, though, they aren't even aware that this information is included with their pictures.
Whether or not you are comfortable with location data being stored in your pictures, it is part of all the metadata stored within your images. Besides location information, metadata is used to store other information such as the date and time the photo was taken, the image dimensions, the camera make and model used , camera settings used for the shot, ratings, keywords, captions, and much more. Clearly, much of this information is desirable and worthy of preserving. Because most metadata can be useful, a good photo editing app will try to preserve it.
However, if an app developer wants their app to preserve metadata, that means they also need to require location services, because location information could potentially be part of the metadata stored in your photos. If an app does not request permission for location services, there is a good chance that this app does not preserve any of the photo's metadata, so you lose access to that useful information.
Some photo editing apps will request permission, but still allow you to use the app even you deny the app permission to use location services. In these cases, the app will only preserve metadata if location services is granted permission.
Unfortunately, Apple makes this requirement seem much scarier to users than it needs to be, due to the confusing language used in the permission popup:
"Appname" would like to use your current location.
This allows access to location information in photos and videos.
Don't Allow / OK
The user who sees this is bound to wonder why a photo editing app wants his current location and answer "Don't Allow" to the dialog. In fact, the app requesting permission very often does not want to use your current location--it only wants to preserve the metadata of your photos, which may or may not include GPS location. However, it must display this misleading, alarming Apple-provided message. Unless/until Apple comes up with a clearer way to address this issue, most apps which provide access to the photo library will request permission to enable location services.