The main source of roster data are the Compiled Service Records for each individual, but these are far from complete. As Driver notes in his introduction, the amount and quality of surviving CSR and muster roll information varies greatly between units, and, for many, the records are silent for the last few months of the war. On the other hand, according to the author, Rockbridge County has the best collection of county records in the state when it comes to its Confederate soldiers, and Driver made extensive use of those materials, as well. To enhance even further the informational value of the rosters, Driver also did extensive manuscript research of his own in addition to consulting census records, town and city archives, newspapers, periodicals, and published resources of all types (including all volumes of The Virginia Regimental Histories Series).
Roster entries most often contain birthplace and date, date of death and burial site, some physical attributes, education level, military service and employment headlines, and affiliations with notable organizations and institutions. Below is a randomly chosen example of what one might typically find:
"Page, Robert Powell, Jr. Pvt., 1st Rockbridge Arty. b. Chapel Hill Dist., Clarke Co., 8/26/46. Att. Oak Grove Academy, Millwood and Episcopal HS, Alexandria. Enl. Gordonsville 5/1/64. Detailed as courier for Col. Thomas H. Carter through 12/31/64. Paid 7/20/64. 5'10", fair complexion, blue eyes, light hair, student. Surrendered Appomattox CH 4/9/65. Farmer, grain and feed merchant, Boyce. On board of supervisors, Clarke Co. and president of Clarke Co. Horse & Colt Show. Senior Warden, Christ Episcopal Ch., Millwood. Member, J.E.B. Stuart Camp, Confederate Veterans, Berryville. d. Berryville 7/26/13. Bur. Old Chapel Cem., Clarke Co." (pg. 232)There is less information for some individuals and a great deal more for others. Though not a regular accompaniment to the roster entries, a number of photographs are also present in the book.
These kinds of reference book projects don't receive much popular acclaim, nor do they often grace award nominee lists, but they can be invaluable tools for those conducting serious research. You might think you'll never need them, until you do, then their existence is a time and labor saving godsend.