On my laptop when importing images it only does one "operation" rather than the two when importing on my desktop. Any ideas why? It's really nice to have both operations (importing images and building previews) working at the same time, I can walk away and all is done when I come back!
Can you be a bit more specific? Lightroom can't show you images without having a preview at all, so what is not done when you come back? Are you perhaps importing with 'Embedded and sidecar' previews checked and you are looking for the embedded previews to be updated? If so, you have to check this: Preferences - General - Replace embedded previews with standard previews during idle time.
If, in the import dialog, you have File Handling > Build Previews set to Minimal then only one operation will occur on import.
Change the settings to Build Previews >
or Smart Previews
and you'll see 2 operations in progress upon import.
Smart previews have nothing to do with this. They are something completely different.