There are plenty of apps that let users store their photos, but the Collections app has a far more targeted purpose, which helps to make it more streamlined and effective than competitors. The app is expressly designed to store images that serve as reminders and inspiration, giving users a quick way to reference the images that they've collected from the world around them.
In a way, the Collections app is similar to a platform like Pinterest in that it gives users a way to keep a repository of their favorite pieces of inspiration. However, Pinterest is meant to be a social network, with users sharing their inspiration boards. The Collections app is meant for users to keep for themselves.