The photo editing algorithms in Lightroom are identical to ACR. Essentially, Lightroom and ACR are the same set of tools and algorithms.
Lightroom is a workflow enhancement tool. It allows you to speed up operations regarding managing, developing and distribution operations by providing integrated tools to allow you to organize, edits, and publish/share your work. Naturally, you don't have to use ALL of those tools (I don't use Book or Web modules). Many people do most of their editing in Lightroom, and then send the photos to Photoshop for more advanced editing, the two softwares are integrated nicely.
I have my own developed system of computer photo storage so I don't need Lightroom for that
It might still be worth your time to investigate the tools in Lightroom, which provide more powerful organizational tools that what you can do with your operating system.
Hi Carey, LR was designed by photographers for photographers. If you are a graphic artist generating assets between In-Design and Photoshop the benefits of LR will be less apparent. As DJP says LR has the same raw engine as ACR ( except last update to graduated filter); so it’s like Bridge and Camera Raw combined into a single package enabling wedding photographers and other volume photographers to sort, edit and categorize images quickly and where necessary make bulk adjustments in a more intuitive interface than ACR.