If you have played poker on your laptop while away from home and want to import the hands you played onto your desktop you can either share the 'Processed' folder so that it is available directly to your desktop via the network or move the files from the 'Processed' folder to a shared folder that you already have set up (or use a memory stick to move the files to the desktop).
Run PT3 on the desktop and use Manual Import to import directly from the 'Processed' folder on the laptop or from the shared folder that you moved the files to.
Manual Import does not move the files that have been imported, so when it finishes you will need to move the files yourself to another folder where you will keep all of the old Hand History files as a backup.
This will leave the 'Processed' folder (and the shared folder if you moved the files before importing them) empty so that next time you repeat this process you will only have new files to deal with.
Once you have imported hand history files to PT3 on both computers the files should all be in one place - the backup/storage folder. Again, I would recommend making a copy of this folder on both computers, but that can be done periodically if you wish.
If you have played on your desktop and want to import the hands to your laptop then repeat the process in the other direction.
Auto Import PT3 on laptop > Processed folder on laptop > [ shared folder on laptop > ] > Manual Import on desktop > move HH files to Backup/Storage folder.