I'm all for "how does this affect play" being the driving philosophy. BUT. Traveller is an RPG that has spawned side games like ground war (Striker) and fleet combat (High Guard, Battle Rider, et al), NOT the other way around.
If fleet combat level detail was all we needed, we could stop at High Guard. It covers "how can this ship fight, how long will it last, and who can it take out" fairly well at the fleet level of abstraction. Fleet combat isn't all of Traveller. Fundamentally Traveller is about the crew of PCs trying to stay alive, so I'm far more interested in ship and vehicle design from the point of view of being able to answer the questions my players ask: "Do we have laser comm that can reach the port?" "No? How long will we need to thrust to reach that range?" "No M-Drive because it took a hit? How long will it take to fix, even to 0.1G?"
As such, Book 2 and HG's approach is not enough if I want to give consistent answer to the above PC questions. At the same time, I *would* like to be able to design a new ship in 5 minutes given the need, and worry about the little details later. Better yet, I'd like to have that 5 minute system in place knowing the details have already been dealt with:
("What does a Type S keep for sensors after it goes to the Reserves? Active Scouts have a Basic Military Bridge plus either the Pinpoint or Limited Survey packages, so I'll assume the add-on was removed." Flip to the 'crunchy bits appendix' and look up 'Basic Military Bridge' for components. Aha, Laser Comm 0.1 AU.)
Do I need to know how many miles of wire went into that bridge? No. Will I want to be able to hit the detailed section and build my own "More Money Than Sense" Nobleman's Bridge? Sure.
Why do I need to know that a radio costs Cr5000 when it's going into a ship that costs MCr80? When replacing that radio after an attempted hijack means the difference TO A PC SHIP OWNER between making the payment and being allowed by the port to lift at all. It doesn't matter that the ship is hugely expensive if the Captain doesnt have that Cr5000 to spare...
The armchair admirals of Traveller fandom are worth some attention, yes, but it doesn't matter how far into the round-offs a component's price tag is if a PC can hold that component in one hand and wonder if he's already dead and doesn't know it because that piece isn't working.