Star Trek: 10 Biggest Differences Between Kirk's Enterprise And Picard's

As mentioned earlier, the Enterprise-D, as opposed to Kirk's ship, had a large number of civilians and children onboard. When the ship was under attack, it needed a way to evacuate all of these non-Starfleet people to safety. This was the rationale behind the Enterprise-D's saucer separation. Saucer separation could be done with The Original Series era ships but the procedure was dangerous and could not be undone, except at a starbase.

Perhaps the coolest, yet most underused feature of Picard's ship, saucer separation could also be used to flank enemies, attacking them from two angles at once. Both parts of the ship functioned completely well on their own, equipped with warp nacelles, weapons, and shields. It would have been nice to see more combat scenarios involving this maneuver.

Saucer separation was only used in a couple of episodes for many reasons. Mainly, it's just because of the high cost of filming the model do it, but also, separation took a long time, as they had to wait for all non-Starfleet personnel to move to the saucer and the crew to split between the two sections.