There are currently two types of groups:
required (the default) and
Changing the type of group can allow you to design more complex workflows by altering how it plays into the rest of your review process.
required group must approve the PR for PullApprove to pass.
This is the default value, but you can use it explicitly if you want.
This feature is available on the business and organization plans.
optional group doesn't directly impact the overall PullApprove status.
They can approve or reject a PR if they want to cast their vote,
but it won't affect your review process unless you leverage conditions later in the process to reincorporate it in a custom way.