The 1701D "Seperation" was originally intended to be used virtually every time the ship went into battle. (After all, got to keep all those civilian family members safe.) However, after they did it on "Encounter at Farpoint", they realized how expensive it was going to be to film the seperated models everytime they went into battle. So it was only done 3 times I believe during the entire 7 season run of TNG.
I have seen the darkness in my soul and shine brighter for it.