The Flush method clears the buffers for the specified log file and cause all buffered data to be imediately written.
When you call Log method, it's typically write the data to the internal system buffer that the operating system writes to the disk on a regular basis. When FlushBuffers property is True, the component automatically write all of the buffered information for the file (specified in the FileName property) to disk.
The flush operations takes additional CPU time which can be critical if you running some server application with tons of active threads. It is recommended to leave FlushBuffers property False, and just call Flush method when it's required.