The Analyze menu > Model Alive command and 
button is a toggle. When this command is enabled, the model analysis updates automatically each time changes are made; that is the model updates without executing the Run Analysis command. The Model Alive™ feature can be especially useful on smaller models because it allows the user to instantly see the effects of any model revision. The Model Alive™ feature will not be as beneficial on larger models with longer run times.
Note: Although the first time the command is enabled you may be asked to save/name the model if it hasn't been saved/named already, your model is not automatically saved each time the analysis automatically runs in the Model Alive™ mode. Rather, it is the user's responsibility to use the File menu > Save command from time to time; otherwise, the model remains unlocked and unsaved.
See Also