QuickBooks Portable file is a higher compressed backup file. It is about 10 percent of a normal back up file size. Of course, the duration for creating a Portable file is much longer than doing a normal backup.
QuickBooks Portable file extension is ended with a ".QBM" and QuickBooks Backup file extension is ".QBB".
Usually, we create Portable file is only when we have an insufficient disk space in our portable media such as USB drive or to send the file over an email or ftp server.
For normal daily backup, we shall use the normal QuickBooks backup file (QBW).