Good maintenance practices dictate that you make backups of your existing data and configurations, before you upgrade your software. This is critical. It is always a priority.
After the upgrade is completed, and you are sure that everything is working properly, say a month later (make sure the usage period includes the complete set of features upgraded), these backup files should be removed. There is no longer a need to have these files to go backwards in case of errors. All that they are doing is taking up space.
Many times I have found backup copies on systems, dating from upgrades, that are years old. Cleaning out these old, outdated, backups can free up an amazing amount of disk space.