I imported about 1500 images ( 36 mpix raw ) into Lightroom. Started the import off, went and did another errand and when the errand was complete...maybe 10 or 15 minutes, all my images were in Lightroom with previews...ready for culling. I then use the rating system and group them by rankings...the bottom ranking gets deleted.
I guess if you are used to culling during import...but I do deal with large number of files and don't see the need to cull during import. I rank...then review the lowest rank to ensure they need to be deleted...and with one quick command, delete all those lowest ranked images. Now not only are my images culled...but they are also ranked with the one's I feel would make prints having the highest rank. Works good for me, but I understand others have their ways.
Once again ... it isn't a matter of 'culling' during the import process per se, it is a matter of selecting only the select few (relatively speaking) images needed right this minute for immediate delivery so as not to waste precious time for images that, while still valuable enough to retain, are not needed immediately for client use.
This is where if Adobe would implement a request many of us have been asking for since shortly after v1 was introduced ... where Lr would only import images tagged in-camera ... just like Photo Mechanic has done for well over a decade and Aperture offered well over five years ago ... life could be simpler for a significant number of users.
Perhaps you should not judge the workflow of others by your own personal situation. Sure, 10-15 minutes might sound like a very short period of time ... and you have the luxury to run errands during the import, other folks may have much more pressing concerns. Sometimes it is relevant to consider the time constraints other folks must contend with.
What if you are working a Division 1 college football game with three other shooters? The group of four has accumulated a couple thousand images on four or more cards from the first half action. Now you only have a total of 15-20 minutes to select the cream of the crop of couple dozen images for an online news gallery and the early edition print run. You need to import, crop, process, caption and keyword (to AP style) and upload to your publication's server so you can return to the field to shoot the third quarter .... then you do it all over again at the end of the game so your publication can get the presses rolling for the late print edition and the followup stories on the online edition. ... then you do it a third time for the images captures from the post game celebrations or disappointment and the press conferences for the coaches and players.
Yep ... going through the entire workflow at least three full cycles in about as many hours.
I'm sure my clients and editors would love it if I told them they should hold the presses because I have to go run an errand while I wait for Lightroom to churn out thousands of previews I don't need because chez doesn't see the need to 'cull' during import ...