Best method for combining assemblies

[theAVator]

If you have a large vehicle that is composed of a number of assemblies, what's the best way to combine all of them into one Keyshot file?

1. Import all of the 'native' assemblies into one file.
or
2. Import each assembly into its own KS file, save as .bip, and then combine all of the .bip files into 1 file.

Is one method more efficient than the other?
Thanks!