I am designing an app with some forms. I have looked at other Cocoa apps to see how they handle the submission of forms. Some apps don't have a submit button and update their backing datastore (or whatever) when, say, a control loses focus or a window is closed. Other's however use a submit button. Is there a rule or heuristic for when to use a submit button and when not?
Anything that makes the user be afraid or have any doubt is a bad thing for UX and conversion rate.
As the biggest part of formularies has a submit button is natural the user expect it. Then if you don't have you will lose submissions.
But if you truly believe that your formulary doesn't need a button because it's a special formulary with unnormal usability and your user don't expect it you should try to remove the button but do it and measure to compare.
P.S.: If you try to convince me that the form doesn't need a submit button, you will rarely do it because I still thinking strange don't have a save button on a Google Docs.