The Sovereign class starship can separate into two parts if required. This is not a practice that is often undertaken, but is available in times of emergency. The Galaxy class starships have to do this more regularly due to their immense size, but it was presumed that this would not be a regular requirement for the Sovereign class. Obviously, once separated, only the secondary hull has warp capability, although the primary hull or “Saucer Section” is still equipped with warp capable auxiliary craft in shuttlebay 1 on deck 7. This image shows the Sovereign class starship separated into two parts:
Also notice that the shuttle bay 1 platform door is open in this image. It can be seen in this next image that the platform is now closed, and auxiliary craft have to enter and exit the shuttle bay using the port and starboard auxiliary doors shown at bottom right:
One purpose for separation in this class of vessel is that it can be used to create two vessels for attacking an enemy ship, creating a scenario where the opposing vessel has to now contend with two ships rather than just one target.
This is an image taken from the Pharaoh’s MSD, which clearly shows the separation plane running through the ship: