Question about moving .lrcat in Lightroom

[Leftyplayer]

Scenario - From my Desktop, I 'export as a catalog' in Lightroom and then move that catalog to my laptop (I've included the previews and the digital negatives). Now I have the originals on both computers.

If I now make changes to photos on my desktop that i want to also use on my laptop, do I have to export as a catalog again including the negatives and previews? Or can I export with just the changes? Once exported (without negatives, if possible) would I import THAT new .lrcat into the laptop catalog? Would it be done any differently than the "regular" import (since that time I brought in negatives and previews, but this time I'm only bringing information about changes made). In other words, would the program know to apply that information to the negatives already there?

Would this be an efficient way to transfer information back and forth between laptop and desktop without the use of an external hard drive (which I do use for backup of originals). Any pitfalls to this process that I'm not anticipating or understanding?

Thanks for any enlightenment you can provide.