So, what do you consider to be the most important BOFF 'seat' on a ship? A Cmdr station, a Lt. Cmdr station, a Lt. station, or an Ensign station?
Most ships have:
The exceptions mostly lie in the BoPs, which drop the last ensign slot.
For me, here's how I see it:
The 'big' Cmdr slot acts as the main focus of the ship. Regardless of anything else, the Cmdr slot pretty much determines how you want to run the ship. Even on a ship like the Recluse or a BoP, you still are gonna choose something specifically for your build, even if it is a universal, and the ships are still geared more towards something in them to begin with.
Lt. Slots are generally the 'standard issue' slots to me. If the ship is heavily engineering, it'll usually be given the 'standard' Lt. sci and tactical slots. It's pretty much a given, nothing really ever surprising here.
Ensign slots help lean the ship a little more towards one area, and can act as a nice balancing point for some ships, but can also be a hindrance on ships that already have two seats of one class already, like the Defiant-R having an ensign tactical even though it already has a Cmdr and Lt. Cmdr tactical compared to the normal Patrol Escort, which has an Ensign Engineer, helping it live a little longer.
So to me, the Lt. Cmdr slot always really helps the ship lean greatly towards something as well. Because you have usage of another 'big' ability. Like most escorts have a Cmdr and Lt. Cmdr tactical, letting them use three 'big' tactical abilities, such as a Torp spread 3, BO 3, and Omega 3 for example.
But say...the Armitage and Multi-Vector (good, straightforward examples). They both have Cmdr, Lt. and Ensign tacticals, giving them 7 tac abilities still, but losing that third 'big' tac ability regardless, and in turn gaining a 'big' engineering or science ability, like maybe an EWP 1, or Gravity Well 1.
This also puts them more towards those classes, making them more attractive to players of said class, because it means they can deal damage, but also still have some of the usage of the abilities they're used to having on their normal ship types.