"An animation file based off the .FLI format, but supports larger movies and other additional features; contains a movie clip created by
Autodesk animation software, such as *Animator Pro*; images used in the animation are compressed with RLE compression to reduce file size."
It's useful to folks who work with Animator Pro and if you are ever given some to work with, you can open it in QuickTime Player and convert it to a format that is accepatable to FCP.