Typically LiveCycle ES Forms is used when you want to render forms to users via a web browser. That is, you render interactive forms to users who then fill in the form and submit the form and data back
Forms is able to output new transformations -- such as form guides. Form guides are flash-based forms.
As far as Ouput - you can convert a non-PDF/A document ot PDF/A as well as output PDF/A documents.
Also - LiveCycle Forms no longer outputs non-interactive PDF documents. This functionality is also covered by the Output service.