First, you can use the Concordance tool on any book in your library. That never occurred to me.
Second, you can use the Concordance tool to view References, which is exciting. You can see just how frequently (or infrequently) an author cites Scripture, church fathers, etc.
Third (and this is really interesting), you can use the Concordance tool to view Works Cited, creating a live bibliography at your fingertips. I'll tell you why this means so much to me. As a preaching pastor and not a theologian, I don't have time to be knowledgeable about every author or resource. When I find an author to be accurate and true to the Scriptures, I have a tendency to trust the sources THEY trust. Using the Concordance to examine Works Cited tells me (generally speaking) who the author of a commentary or monograph trusts, which helps me as well.
That's all; have a blessed day!