Additional features? LR and ACR have all the same editing functionality. You don't lose anything by adjusting a RAW file in ACR vs LR. You can still get access to the original image. You can save snapshots in ACR, just as you can in LR.
It is my understanding that LR and ACR have the same processing pipeline, so yes, the editing results are identical. LR, however, has a different, and in my opinion, significantly more feature-rich interface to these editing capabilities.
A couple examples:
LR maintains a history of all changes. ACR does not.
LR has a robust Before/After compare mode while you are editing. You can set any history step or snapshot as the Before, then compare with a single keystroke. You can compare split screened, etc. with synchronized zoom and pan. None of this in ACR.
In LR you can define two adjustment brushes with different size, feather, and flow characteristics and a third for erase and easily switch between them. You can use your mouse scroll wheel to resize the brush and its feather. Not in ACR.
In LR while you are editing you can display the results in realtime on a second monitor. You can even have that second monitor in Loupe / Compare / or Survey mode, zooming and panning independently of what you're doing in the develop module, all the while having your edits show up on both monitors. ACR, not so much.
These are just a few examples of LR's features available when editing; they barely scratch the surface. I used to be a pure ACR user for developing images because of LR performance issues. With LR4 the editing performance now rivals ACR (for me, at least). The more I use LR to develop the more I appreciate its power for enhancing and streamlining the workflow.