You do not see tanks with armoured cars attached that they can drop to do scouting. Aircraft carriers do not have missile frigates in the hangars taking up space, and B52's dont carry F16's for air cover. These are independant units which can work with the larger stuff in a combined force, they dont need to be carried 'just in case'. Citing one-off experiments which never proved practical proves nothing. If you are allocated 100,000 tons of materials to build the best battleship you can, you dont build a 75,000 ton battleship and a 25,000 ton cargo ship that fits in the back of it so that it doesn't need to visit ports so much. You already have cargo ships, just as you will already have frigates and fighters and so forth. You compromise your primary design and waste resources. Belisarius has designed a really nice looking ship, and is in danger of wasting it so he can fit another separate ship in the back of it. I think it's another manifestation of the syndrome where people feel that a single Trek ship always operates alone and must be capable of performing every role in the fleet.