As a side benefit to transaction logging, the log file also makes it possible to "replay" (or "recover") all file updates (whether or not part of a "transaction").
As an example of the recovery feature, let's say you do nightly backups, after which you erase the log file. Half way through the day, somebody accidentally erases one of your ISAM-A data files. To recover it, you would restore all of the ISAM-A files from the previous night's backup (taking care not to overwrite today's log file). Then you would replay the transactions from the log using:
.ISRCVR logfile
