AI is the default graphic format used by Adobe Illustrator to save image data, and image files encoded using this format contain single-page vector drawings that can be easily magnified without losing any image quality.
To be able to edit their AI files, users will have to use Adobe Illustrator or choose one of the available graphic editors that come with built-in support for the AI image format.
However, not all compatible apps will offer their users the option to correctly manage the image layers containes inside AI files.
AI editors will allow users to quickly apply graphic effects onto their pictures or to overlay custom watermarks.
Moreover, some of these apps can also be used to export the adjusted AI images to other graphic formats.