The main developer James Bennett has discussed his reasons several times on multiple venues, but the FAQ in the Read the Docs for django-registration gives details in "Does django-registration come with any sample templates I can use right away?"
https://django-registration.readthedocs.org/en/latest/faq.ht...
Other people have provided good baselines to work from, the Djen of Django provides explanations with their samples:
http://agiliq.com/books/djenofdjango/chapter5.html#reusable-...
(note I haven't upgraded to 1.0 so not sure if there are any incompatibilities)