I reinstall emacs by compiling its source and then
sudo checkinstall. I found
checkinstall creates a file
-rw-r--r-- 1 root root 44628516 Apr 22 19:19 emacs_24.5-1_amd64.deb -rw-r--r-- 1 root root 56991208 Apr 22 19:19 backup-042220151919-pre-emacs.tgz
checkinstall create a backup file regardless of which software it installs, or it depends on specific software (e.g. emacs) (maybe depending on the specific Makefile?)?
What is the backup file for?
Shall I keep it, and when can I discard it?
How shall I use it in case it is needed?