Here's the number one problem in the South: almost all courthouses were built of wood until the 1920s. My father's family's home county had the courthouse burn THREE times -- in 1875, 1899, and 1933 -- and Sherman had nothing to do with ANY of those fires! It sure did play hell with the records, though!
Many birth, death, and marriage records have been reconstructed from family Bibles, newspapers, and graveyards. But it's spotty, and frustrating.
As far as I know, the only courthouse fires that effectively blocked our genealogy research were caused by Sherman's troops. That is not to say that some Southern courthouse fires might not have caused lost records for my family prior to the war, but if so, the fires didn't stop us from being able to trace most of my family branches into the 1700s.
However, genealogical research on my wife's ancestors is particularly difficult. All of them lived in Sherman's path. My Georgia in-laws hated Sherman with a passion. Their parents had seen Sherman's troops come onto their farms, and I suppose they had reason to hate him. That strong feeling passed down through the family for over 100 years.