I do a lot of my editing in ACR with a some help from Photoshop and NIK Collection - (mostly in Viveza)...
From what I have been able to garner from various sources, the major advantage of LR over using ACR and PS is in cataloging your images.
If I am correct, everything (with the exception of cataloging - and I am not really sure of that) can be done using ACR because ACR is actually akin to the Develop Module of LR...
The YouTube Video "Scott Kelby's Photoshop For Travel Photographers"
https://www.youtube.com/watch?v=LIt1cDw5lLI
is a good intro to working with ACR with the Caveat that Kelby is working with an older version of ACR in this video...