Sometimes it is a lot easier to pick up a book of compiled records than it is to go to the various courthouses to get copies of the original documents.
These resources can be very useful tools but don't make the mistake of relying too heavily on them.
There are books of marriage records, tax records, land records, wills and cemetery surveys available for almost every county in the United States. These books are only as good as the compilers that put them together.
I am going to use Lincoln County as an example. Lincoln County happens to have more published compiled records than McDuffie County does. Here are a few of the compilation books available:
Lincoln County GA Marriages 1806-1955, compiled by J.B. Turner and L.B. Butler
Lincoln County Cemeteries, compiled by Betty Sue Dunaway Burch and Larry Raymond Butler
Lincoln County Genealogy and History, compiled by Robert S. Davis Jr. and James E. Dorsey
History of Lincoln County, Georgia, compiled by Clinton J. Perryman
You can find a lot of great information about your family without ever leaving the comfort of your easy chair. It just so happens that these particular books were written by competent genealogists that accurately transcribed the available records; however, not all compilations are as trustworthy. I try to have all the available books for each county that I am working in.
Unless I know personally the genealogist who compiled the book, and I have spot checked the records, I can not say whether or not the compiler did a good job or not. I have found many books with errors in them. I use these as reference books only. If I find useful information, I try and go back to the original source cited and get a copy for my files. For example, if I find a marriage record that is of interest to me in one of these compilation books, I will then contact the courthouse and obtain a copy of the marriage license.
The marriage license is a more credible piece of information than a compilation book.
If I am using a compilation book as a source, I cite the book as my source and not the original record. For example, James Tyler married Mary Ann Frazier in Lincoln County on 11 Aug 1831. If I am using the transcribed record in a compilation book I would cite it as:
J.B. Turner and L.B. Butler, compilers, Lincoln County GA Marriages 1806-1955 (Privately printed, 1996), 28.
But, if I had James and Mary Ann's actual marriage license in hand, I would cite it as:
Lincoln County Marriage Book G-1, 1806-1829, Lincoln County Clerk's Office, Lincolnton, Georgia.
You must cite the source you used. Do not cite the original marriage record unless you have seen it yourself or have a copy of it in your possession.
I encourage you to find all of the available books for the county you are working on but at the same time I also encourage you to use this information as a starting point in your research and not the definitive answer to your genealogical dilemmas.