At the beginning, most people who begin bjj have a very similar style to each other (just learning fundamentals).
But very quickly, people will realize that they tend to prefer playing a specific type of game that may or may not work well for other people.
Many things determine this:
My opinion on this would be to learn as much as possible and to develop a system around your strongest moves. (i.e. if you play de la riva guard, have 3 or 4 moves you can do from a failed sweep attempt that can be launched right away).
Eventually when you become a black belt, you will not have just a system that works around one area you are strong at, but you will be strong at most positions. In a way, it is rinse and repeating the above process for different positions.
now a video of Marcelo Garcia grappling Ben Askren, notice the difference in their styles.