If you're a committed photographer, you probably use a powerful tool such as Adobe's Lightroom or Photoshop to work with your pictures. But not everyone needs apps like this, which have steep learning curves, and not everyone shoots enough photos to spend the time and money for this type of tool.
Most people who take pictures just want to do some simple editing, and you can use Apple's Photos app on both macOS and iOS. But between those two alternatives, the $4 Enlight is a powerful editing tool for iOS that anyone can use. Its tap-and-drag interface gives you access to a number of filters, presets, and tools, and you don't need to spend a lot of time learning how it works.