• fast processing of multiple images including the ability to synchronize development adjustments across multiple images.
• non-destructive parametric edits throughout, so you can re-develop and revisit images as you wish.
• starring and ranking schemes to help you in selecting out keepers and culling duds.
• ability to create multiple virtual copies with different processing, cropping, etc., and compare them side-by-side.
• easy export in multiple formats/sizes, etc., from the same base developed RAWs.
• a thumbnail browser and integrated workflow platform, allowing you to launch Photoshop or other pixel-editors like the Nik Collection, and then return to Lightroom to the edited image for final export.
• powerful cataloging and indexing and keyword creation and searching (although I stupidly don’t use this capability!)
• good dual-monitor interface, so for example I have my 30″ wide-gamut screen set-up as the main image loupe with the only the image full-size on it, and all the panels, etc., are on the second laptop display.
• presets which are freely found on the web for all flavors of development process type effects, for example including split-tone, de-saturation, B&W, etc.. etc..
• an infinitely-flexible digital grad filter tool. [You can buy a Cokin or other filter set or get Lightroom with all it does for around the same and carry less in your camera-bag. The only optical filters I now have in my bag are polarizer, ND8, and ND400.]
• a good print module, slideshow module, and web module for easy export of your images for viewing by others (maybe I am understating the power of these).

In a combined workflow, Photoshop (I am describing Creative Suite) then gives you:

• Pixel-based editing and saving.
• Cloning for detailed removal of unwanted objects in an image.
• Selections, masking - for area selection, color-range selection, etc.,.
• Mask editing like blur, feathering, fills - all great for local work within the image.
• Layers and adjustment layers for combining images in composites or blends. Adjustment layers for discrete control of many image attributes (brightness, contrast, levels, curves, colors). Each layer or adjustment layer can have a mask and opacity to keep the change and extent local to only one or more parts of the image.
• Layer blend modes with opacity control for more complex combinatorial effects (like darkening, lightening, overlaying, texturing, re-coloring one image with another).
• Ability to resize and extend images or layers.
• Ability to transform (stretch, skew, etc.,) images, parts of images, or masks.
• Algorithmic image combination like stitching and alignment.
• Creation of shapes for selections, masks, gradients.
• Comprehensive set of filters, including basics like blurring, sharpening, as well as more effect-like for outline, painting, drawing type effects. Then there are many plug-in filters available to help with selections, picture effects (again which can be as simple as sharpening). These can also be used together with layers and opacity to give real detail control throughout the image.
• and more... like text adding, etc., but some of these step you more into the world of graphics design not photography.

So, it depends on your photography, but if your main emphasis is just taking pictures and doing minimal detail editing within the image, then LR gets you pretty much all the way there. If you really want to squeeze the very, very best from every part of your image with real local control, then you need go across to Photoshop and use masks and selections and all the other powerful tools that Photoshop provides. Photoshop is then definitely for blends and composites as LR has no capability for that (other than with external editor plug-in).