Automatically opening or saving documents with the General preferences
The General preferences are the first pane in the preferences window, available by choosing Preferences from the OmniPlan menu.
Automatically opening or creating documents
When OmniPlan starts up, it can summon whatever documents you were working on the last time you quit, and it can create a new document if you don't have anything else open. These settings are both in the General preferences pane.
Automatically saving a document backup
OmniPlan automatically saves a backup version of your document as you work on it, in case there is a crash, power failure, or some other misfortune. The setting for how often to save a backup is in the General preference pane. You can always get back to the last deliberately saved version of a document by choosing Revert To Saved from the File menu. If you close a document and choose not to save it, the automatically saved backup version is discarded.
When a document is saved to the disk, the red close button is empty 
When you have unsaved changes, a dot appears in the close button 
Something bad happens 
When you reopen the document, the last auto-backed-up version appears as a document with unsaved changes. You can continue working with the backed up version, or you can choose Revert To Saved from the File menu to go back to the saved version. 