remember that with carbon, the ability to crank the seat post binder bolt down is limited (typically 3 to 5 nm) to avoid damage to the carbon frame and or seatpost which means the clamping force is limited.

Clamping force is friction and as the friction is reduced, you need to add some additional friction to prevent slippage, which is where he carbon paste comes in. put a piece of sand paper flat on your work bench and press down lightly and try to move it...it does not move, but if you flip it over to smooth side you need a lot more pressing force to keep it from moving. same principle on the post.

Assembly wording simply means you use it when putting the seatpost in (or assembiling it)

this was never needed or used before carbon