What is the purpose of helm delete --purge

Recently they've finally managed necessity of --purge by replacing helm delete with helm uninstall. There appears it works fine now

Just to note as of helm v3 --purge is default behaviour. You no longer need the flag

If you want to keep any history (aka the behaviour of helm 2.x's helm delete without the --purge flag) you now need to use --keep-history eg helm delete nginx-ingress --keep-history

When you do helm delete $RELEASE_NAME it deletes all resources but keeps the record with $RELEASE_NAME in case you want to rollback. You can see removed releases via helm ls -a. Whereas helm delete --purge $RELEASE_NAME removes records and make that name free to be reused for another installation.