When circular logging is enabled, you cannot run incremental and differential backups of Exchange databases and storage groups, or run backup jobs for which continuous protection is enabled. These types of backups rely on a complete history of logs.
When circular logging is enabled, transaction log files that have already been committed to the database are overwritten, preventing the accumulation of logs. The log files are overwritten whether or not a full or incremental backup has been run, and a history of previous logs since the last full or incremental backup is not maintained.
When circular logging is disabled, transaction log files accumulate on the disk until the following occurs: