Police Check on the Sponsor for a Partner Visa.

The primary reason for a Police check, on the Sponsor for an Australian Partner Visa, appears to be to protect the visa applicant.

Some wording from the Immigration website on the subject.

We will not refuse a visa application if you have a conviction for a relevant offence but no significant criminal record but we will disclose any convictions for relevant offences to the visa applicant to help them make an informed decision about continuing with their application.

We consider you to have a significant criminal record if you have been sentenced to:

death.
life imprisonment.
imprisonment of 12 months or more.
2 or more terms of imprisonment that total 12 months or more.

https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/prospective-marriage-300/additional-sponsorship-requirements

The Sponsor is normally an Australian Citizen, and they cannot be refused entry into Australia themselves.

Sponsor ai10

Sponsors who are Foreign citizens, but Permanent Residents of Australia, may face issues with their own police checks, and these may be well advised to get advice if a police check reveals new information.

Some statements from the Department of Home Affairs regarding…

Sponsor Police Check for Partner Visa.

We will not refuse a visa application if you have a conviction for a relevant offence but no significant criminal record but we will disclose any convictions for relevant offences to the visa applicant to help them make an informed decision about continuing with their application.

If a sponsor has convictions for a relevant offence and a significant criminal record we must refuse the visa, unless we assess that it is reasonable not to.

We will consider all the circumstances of the application when we make this assessment. These could include but are not limited to:

how long it has been since the sponsor completed their sentence.
the best interests of any child or the sponsor or primary visa applicant.
how long the sponsor and the main visa applicant have been in a relationship.

What is a relevant offence?

A relevant offence is an offence against a law, either in Australia or overseas, involving:

violence, including murder, assault, sexual assault or the threat of violence.
harassment, molestation, intimidation or stalking.
the breach of an apprehended violence or similar order.
firearms or other dangerous weapons.
people smuggling.
human trafficking, slavery or slavery-like practices (including forced marriage), kidnapping or unlawful confinement.
attempting to commit any of these offences.
aiding, abetting, counselling or procuring such offences.