Explicações no universo
O Manual Técnico da TNG (considerado uma fonte canônica de informações sobre o universo da jornada) oferece várias razões pelas quais as separações eram raros:
A sequência destina-se a ser utilizada apenas em "emergências"
The USS Enterprise consists of two spacecraft systems integrated to form a single functional vessel. Under specific emergency conditions, the two vehicle elements may perform a separation maneuver and continue independent operation. The two elements, the Saucer Module and the Battle Section, are normally joined together by a series of structural docking latches, numerous umbilicals, and turbolift pass-throughs.
As separações danificam o navio
The latching system has been designed to accept a failure rate of 1.5 latch pairs per ten separations; in the event a single pair fails to seat properly within its passive aperture, the structural loads can be shared adequately among the other latches.
...
Should any key umbilicals or turbo paths show a failure condition at the vehicle interface, the computer will close off the affected elements at the best possible points upstream of the failure. Hardware and software failures will then be dealt with later, once the emergency situation is resolved. Crews on both sides of the vehicle interface monitor the progress of the separation sequence, and are then on standby awaiting reconnection duties.
Também vemos alguns raciocínios no próprio programa:
Separar a nave realmente prejudica a capacidade da nave de manobrar em combate aproximado.
SHELBY: There's one other recommendation I'd like to make, Commander. Separate the saucer section... assign a skeleton crew to create a diversion...
RIKER: (shakes his head) We may need power from the saucer impulse engines... - TNG: Best of Both Worlds, Pt I
Separar representa um perigo potencialmente 'fim da missão'
E finalmente, vemos em TNG: Encontro no Farpoint , Pt I a dificuldade de Juntando o navio manualmente. É lógico que uma falha de computador em um momento crítico (e vamos encarar, acontecem todos os outros episódios) poderia danificar gravemente as duas metades da nave, imediatamente terminando sua missão e resultando em uma viagem embaraçosa para o Stardock mais próximo, para que o equipe de reparos pode rir de você consertar a nave
Fora das explicações do universo
Houve várias razões fora do universo, em grande parte relacionadas à despesa relativa das sequências de filmagem, falta de modelos e o tempo extra de contar histórias necessário para ver a sequência em si e o script extra necessário para explicar as regras de como ocorre a separação :
Eles só tinham um modelo (obsoleto) que poderia realmente separar, limitando severamente sua capacidade de fotografar
Though less favored by Rob Legato and Dan Curry and largely unused since the appearance of its four-foot cousin in season three, the original six-foot Enterprise model had to be hauled out of storage for the ship-separation sequence in the Borg battle, since it was the only version built in two sections. The various battle effects and Borg visuals are motion-picture quality, but again TNG struck out with the Emmys for special effects. Part 2 was nominated, but it won no awards in that category. The episode did snag Emmys for sound editing and for sound mixing, as well as a nomination for art direction. - TNG Companion
Diminuiu o ritmo
Aparentemente, houve várias tentativas de escritores de adicionar uma sequência de separação de navios, todos abatidos pelos produtores.
Ironicamente, essa tendência para a sequência de separação consumir o tempo foi realmente útil no episódio piloto, estendendo-a para o tamanho do recurso.This was an opportunity to utilize those often ignored shipboard families that Shearer initially pitched to Fontana, and it was this story that helped win her a spot on the writing staff. A subplot [in TNG: When the Bough Breaks] involving ship separation and the saucer being held hostage was phased out to focus on the main story. TNG Companion
According to Justman, both the ship separation sequence and a touching scene in which an aged Admiral McCoy meets Data were a help in filling out what Fontana had intended to be a ninety-minute script. TNG Companion
Por causa do tempo e despesas envolvidos
Notavelmente, o conjunto Battle Bridge foi muito caro para ser construído e o estúdio preferiu não criar conjuntos quando eles poderiam evitá-lo.
During the first few episodes of Star Trek: The Next Generation, saucer separation was intended to be a standard maneuver in combat situations, but was rarely done because of the costs for visual effects and for rebuilding the Battle Bridge; also, it was felt that it slowed down story-telling too much. - TNG Encyclopedia