When your visitor wants to register, you must be sure that the registration form does not contain a lot of extra fields, as it is annoying and reduces the probability of a new user logs into the system. Many people leave the site, if you see complex forms during registration, multiple captcha and other elements.
Thus it would be appropriate to share the form you need to fill in some pieces. jQuery code will not load constantly the same page, and the registration process will look more clear.
This decision not only does not overwrite the original files of Joomla, but also allows you to split the registration form into multiple steps, even with the availability of installed extensions with additional fields in the profile. So you will get all the necessary data about the user of the website, and not immediately load it with unnecessary information.
The division of the registration form painless
A great way to keep the visitor on the page
Free plugin Joomla