These keyboards are very powerful tools, and just like computers, often have multiple ways to get to what seems to be the same end. Yes, it is true that many re-named styles have fairly insignificant differences to the original, and the same end could have been achieved another way. That can be a matter of choice, but it is also more than that. For example, very deep changes can be made to a style, things that cannot simply be done by adding or altering features, and storing those in a registration. For example I can take the bass line from one style and replace it in another, I can change some or all of the voices in a style, so that a trombone phrase becomes a violin phrase, and in fact styles can be created completely from scratch. Just like on computers, the power users tap into all or many of these things, but many people can do all they ever need to do without ever getting into this.
On choice, some people simply prefer that they adjust and re-name a style for a particular song, rather than use registrations. Both can work similarly, but at the same time offer slightly different pros and cons.
And we are all a bit different in our approaches, capabilities and interests. Some members love being able to use other peoples set ups (registrations) for songs, because they feel either intimidated by the process of doing themselves, or simple think it saves effort. Then again some will never have done that at all. In over 15 years of owning an arranger, I have never imported someone else's registrations.
Couple of things to take note of when using registrations from other people.
1. Registrations are essentially just files that point to features and their settings. So unless they are all in the same place on your keyboard the keyboard can't find them. Its like me saying the pens are all in the top right hand drawer on my desk. That will probably not be true for your desk. This can lead to problems when you import registrations.
2. They are just someone else's idea of what works on that song. That doesn't mean it's good, or better than you can do yourself. And making music is a creative not a mechanical process, and there are always many different ways to play a song.
Mike