When you want to build a ship, you certainly want a full list of parts, but loading a parts list is much faster than loading the parts! You only need the parts fully loaded when you're actively trying to put them on a ship.
That said, most of the time you'll be using similar parts to parts you've already used on other ships, and therefore those catalogs will already be fully loaded.
so your loading couple of KBs of data for a part you want to use, instead of several GBs of data of all the parts that go along with that one part? I think The division is doing something like this with there "no loading screens". where as you load up once and as you walk around the world it loads that sector you are in and caces the one you left. The only issues I have had with this are falling through the ground and 8 bit graphics for about 10 secs while everything calibrates.
