Dear Pino,
thank you for your comments.
Before I purchased the present CVP309PE, I had for about 20 years Korg keyboards, with hundreds and hundreds locations available on board (internal HD drive) for MY styles.
I'm getting the same availability of space thank to the USB port of my Clavinova.
I made a few Registrations for styles also, whenever the modifications to an existing style are minor.
But whenever I like to go more deeper (for example: change Rhy1 from snare to drumstick; or lower the volume of the kick drum only without altering the volume of the other components of the drums; mute or change the volume of one or more tracks of one part only), I found that working in Style Creator give much more opportunities of fine tuning a style.
I like very much to use registrations for having my own set of voices that I can access instantly while playing real time, in addition to the 4 OTS.
In this respect, I found very useful to may change the OTS (often I don't like the voices selected by Yamaha for a particular style), by saving my choice into the Style.
Anyway, It's a matter of personal preference, of course.
Thank you
Angelo