[Zope] what is the difference between the enctypes

Good morning, By experience I learned that I have to use an enctype of "multipart/form-data" when sending a file. "Normal" forms use an enctype of "x-www-form-urlencoded" (which is the default) Now my question: is there a reason NOT to use always multipart/form-data? In http://www.ietf.org/rfc/rfc2388.txt I did read that the effect of using the same field-name more than once is not defined. Would that hinder Zope to create a records out of a set of actually named fields?? Robert