As a teenager I think deckplans got used either when exploring a possibly prize bounty or during combat to refer to where crew were, damage control, leaks, fires, survival that kind of thing.
Since making 3D maps for Action RPGs and growing up, I think a number of things are in my mind when designing ships. What people want, what is new (if possible), what is plausible, logical and makes sense. Also I think more about exploring inside the ship and combat, every day life, how to make it interesting and not like turnkey motel inside. What surprises, traps, treasure, chokepoints, defensive areas there might be. I think about security of the ship and ask myself, would I want to fly this ship. I try not to design perfect ships but build in vulnerabilities, chinks in the armour etc.