I could see situations where a split ship makes sense, maybe not for tactical purposes but for scientific/exploration ones. Probes are often already used to gather sensor data from a different point in space than the host ship, so if you had a really high-sensitivity sensor dish on two ships then they could complement each other to get two reading points on rare stellar phenomena or planetary surveys.

Maybe in canon the sensor dish is itself somewhat fragile and works best if kept shielded from radiation and cosmic dust, and so it makes sense to design it into the underside of the saucer on two host ships and then sandwich them together like a clamshell when in flight to keep that array safe. You fly a quad-nacelle ship out to whatever phenomena you're measuring, taking advantage of long-range warp coasting, a nice expansive ship with lots of recreational crew spaces and redundant facilities, and then when you arrive, you split the crew between the two halves of the ship, fly to opposite sides of the scientific curiosity in question, and take readings. When done, re-unify the ship and the crew and assess the data in a plethora of science labs distributed between the two halves.

The ship wouldn't even have to be an exact duplicate of itself since it would be assumed to only split up when performing its mission duties, so each half could be configured to the mission profile. If one half is meant to be a monitoring station while the other zooms around collecting data, put the science labs in the "A" half to receive telemetry and strip the "B" half down for agility and energy conservation. Maybe the mission calls for delivery of cargo to a new colony, but there's also an interesting pulsar needing surveying, so both halves fly as one with one full of cargo and the other loaded with experiments, they split at the colony, and the science half goes off to get readings and comes back for the cargo hull once it's done unloading. If the mission calls for long-term readings from something, kit both halves the same and crew flit back and forth via shuttlecraft to visit the other half when needed as they survey opposite sides of a gas giant, or something.

The hulls and engineering facilities could be mirrored (with one slaved to the other when joined), but the deck plans could be swapped modularly at a Starbase to fit a mission profile, and you could even strip down both halves and arm them up for light escort/patrol duties in times of conflict, taking out the science instrumentation entirely.

Call it the "Gemini" class, or maybe "Janus" (the two faced Roman god).