Basic (?) question: apart from the "cataloguing" side, is there something that LR does better than PS, or is there something that LR does and PS doesn't ?
The Develop module in LR is pretty much functionality equivalent to ACR (Adobe Camera Raw). There are a few features in LR you can't find in ACR; virtual copies, proof copies, unlimited history and so forth. But you can bounce back and forth between the two if you wanted to (assuming both were on version parity).
Then there are the various modules which may or may not be important to you. For me, the Print module is worth the price of admission alone. Photoshop has, from day one, been a
'one image at a time' affair and if you need to print a lot of images, it's really slow! The Print module is much more efficient in so many ways. We can go there if a printing workflow is something you need to discuss.
Like printing, if you need to prep lots and lots of images, LR is vastly more streamlined. Say you want to take 100 raw's and process them to a smaller size, convert to sRGB, create JPEG's and strip out some EXIF data. Select, pick an Export Preset (build it, use it as often as you desire); done. In Photoshop, you'd have to spend the time opening each 100 images just to start the process (and no, droplets are not the answer; PS still has to open each image before you can do anything, one at a time).
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Andrew Rodney
Author: Color Management for Photographers
The Digital Dog
http://www.digitaldog.net