Form without a form routine (ENTRY_NEU)

Hi,

I have few queries in form:

1. Why do we have to give a form routine while configuring a form with a output type ? What does return code means in form routine ?

2. Why do we have different type of Form routines, entry, entry_neu, etc. Is it just to save all the routines in one driver and configure different routines to diff output types ?

3. If in my driver program I have only one form routine, is it possible not to mention the Form Routine name in the output configuration ?

4. if I do not create any form routine and still can configure the driver program and form to a particular output type.

-Thnks