MarkB
Legend
I believe it's mentioned somewhere (probably the TNG Technical Manual, as that's where a lot of my early trek lore was gleaned from) that this general configuration of hulls and nacelles worked well to produce a stable and efficient warp field. Clearly it isn't the only viable configuration, but it was a particularly optimal one, at least for larger starships.
I think the division into two hulls was essentially considered a safety feature, allowing for the possibility of separating the most densely-populated section of the ship from the engines and nacelles in the case of critical failure - a quicker and less drastic option than a full-scale evacuation.
That becomes a minor plot point in Star Trek Beyond, when the Enterprise's 'neck' is severed just below the saucer section's detachment point, and the saucer section's independent propulsion systems won't kick in because it still thinks it's linked to the engineering section.
I think the division into two hulls was essentially considered a safety feature, allowing for the possibility of separating the most densely-populated section of the ship from the engines and nacelles in the case of critical failure - a quicker and less drastic option than a full-scale evacuation.
That becomes a minor plot point in Star Trek Beyond, when the Enterprise's 'neck' is severed just below the saucer section's detachment point, and the saucer section's independent propulsion systems won't kick in because it still thinks it's linked to the engineering section.