This interface defines which format (width and height) your images can have. For example your images can have such formats: full (default), large preview, small preview, etc.
These formats you can use in Flmngr.pickFiles to require some specified sizes of images user selects. For example, you ask user to select images for photo gallery and require to have both full-sized image and image preview for each photo. User will select only original images and your app receives all required formats transparently.
The list of formats will be used in Flmngr browse dialog (called by Flmngr.browse) method to group images by formats: user will see only original images.
pickFiles also uses
Maximum height in pixels for this format
Maximum width in pixels for this format
Suffix for file names used to save an image with this format. For example suffix
-preview will save resized
Title of this format