Default will only work if the button has the focus. Since user is entering data, I suspect the last control edited will have the focus. User would have to give or code programmatically set the focus after the last control is edited, which won't work either if the user can/will edit controls in any random order.
You don't need preview on form, unless as noted, any form controls also have key events. Even then, it would depend on which you want to have priority. If you set it and forget and put key events on a control later, the form key event will fire first, which may or not be what you want, such as if the key event was to close the form. That's not something I'd ever do, but am just throwing it out there for an example.
