I am not an active, but (hopefully) soon-to-be active STA GM. I do prepare a campaign for my regular group which I intend to GM when we finished my/our current fantasy campaign.
Deck-Plans were virtually the first thing I searched during this preparation.
This is the trove I discovered. But, as I see, you did, too.
I will need them, to create a better image of the place where the characters live, where they experience their adventures.
In fantasy games, I have maps of the surroundings to show where the adventures happen. If the party will stay within a lager village, or city, I will provide maps so the players can relate the localities with one another (this is probably bad english; hope you understand). If the party (or one player’s character, for that matter) acquires a fortress or some other holding – right, floor plans, you already got it.
For ‘modern’ games (take Vampire: The Masquerade, which I used to play years ago); or take the well-known Shadowrun franchise, I use actual maps (from e.g. the OpenStreetMap Project) and modify them. Etc.
Most of the time, the maps serve the purpose of showing the progress of exploration. Speaking in terms of the GNS-Model, I am a strong S-type person as I am an N-type person. So, when I DM, there is always a world to explore for my players with unique places and persons to discover. The map adds a new dimension to the game because it can show/tell connections of persons, places and their surroundings; if you see that the castle of Sir Lordlylord Castleowner lies directly adjacent to the Hell-Deep Pits of Fiery doom, it will be instantly clear to you, why he so much despises fire-creatures.
You might think that, translated on STA, this purpose would be served well with starcharts and maps of the galaxy, regions of space or even sectors. This is correct. But it is, in my opinion, not enough.
The deck-plan, in my opinion, is central for the perception of the group’s major NPC, the ship. The ship is, where adventures start and end and very often the whole stage where the play is set. It is the home of the characters and, just like Sir Lordlylord and the Firebeasts, ‘seeing’ how far away from another two places are set (or how close they are on the map), you will add another layer of immersion to the game.
Moreower, with deck plans, at least a MSD, you can actually check on which deck cargo bay 3 is located. I am totally fine with people who can randomly shout “Captain, multiple hull breaches on deck twelve, sections forty to forty-five. We need to shield the flank from the enemy fire!” in the midst of a fire-fight. Even if the game is set on a Defiant-Class ship (remember: three decks). I could not. Knowing and seeing where the things are in ‘physical’ relation to another is part of the immersion I need and enjoy.
This is basically how I would use them. As a narrative tool to set the stage. I’d print them out (I’m a paper person; at least one of my players will require PDF, though) and show them to the players, maybe even use them for stategic or tactical purposes (“Three Klingon boarding teams beam in here, here, and here. With the remaining Security teams abord, you can only engage two. Where will the security teams be sent?”) though this might be, because I now played D&D for longer than I did not in my life.
On whishes, I would like to refer you to the Official Product Whishlist here at this forum. My search for “deck plan” got 19 results.