When you do this, you are visualizing, creating a picture, in your mind. Visualizing helps you remember things. This is because memories are usually placed into our brains in picture form. But these are not flat, one-dimensional photos. Memories are more like moving pictures, complete with all the action, thoughts, sounds, smells, tastes, and feelings associated with the original event.
Memories are but one form of visualization.
We all have memories, and we all visualize. But some people visualize better than others do. For some people, who are naturally highly visual, creating pictures in their mind comes quiet easily. Because visualization can do much more than bring forth memories. But that's okay.