What is the purpose of pre-created PodGroups (PG) in Volcano?

[tsingst]

Please describe your problem in detail

in issue 3793,

https://github.com/volcano-sh/volcano/issues/3793

Know "vcjob is not supported to set pg manually, it will always create a pg."
And then i have another question :What is the purpose of pre-created PodGroups (PG) in Volcano?

Any other relevant information

No response

[Monokaix]

It's ususally used for bare pods, such as spark job submitted to k8s, and user should create a podGroup manually to manage a group of pods.