Save Incremental creates a numbered backup copy of the current scene each time you save.
Use Incremental Save to save a backup copy of your scene in the same folder as the scene, letting you keep versions of the scene at various stages of development.
Each time you save, another backup file is created. These backup files are numbered incrementally (for example <filename>.001.mb, <filename>.002.mb, and so on) so that the previous backup files are not overwritten.
You can also use Save As to increment the file name manually with a two-digit number by clicking the increment button (+) on the Save As dialog.
The number of incremental backups created is infinite by default.
See also Backing Up and Archiving Scenes.