In reality Leap updates and Tumbleweed upgrades are not perfect. The normal case is orphaned packages do occur, which is PITA when maintaining many hosts. Thus I keep old packages on one host and copy the orphaned ones to an orphanage.
erlangen:~ # du -hd1 /var/cache/zypp
99M /var/cache/zypp/solv
70G /var/cache/zypp/packages
120M /var/cache/zypp/raw
4.0K /var/cache/zypp/pubkeys
4.0K /var/cache/zypp/geoip.d
70G /var/cache/zypp
erlangen:~ #