It's obviously contributing more data with a high probability of being all signal and zero noise. Some government IDs even include social security #s, but you're adding a photograph.

In the sense of confirming the data, it seems likely to at least attest to the identity being a genuine one associated with that data. Rather than something like a burner phone setup with a bunch of random stuff. Of course people can also have a fake photo ID, but it seems unlikely someone using a totally fabricated existence would be querying for this information and exposing them potentially to closer scrutiny.

For example, checking if you ever had an account at companies mentioned in your data takeout - to spot if someone does shit while using your name/personal information, or some incompetent/malicious clerk mixed up data.

That doesn't verify any data though. At most, it implies a likelihood of having an account, but nothing about the specific data.

If they're uncertain of your middle name for instance, uploading your ID just confirms that they had it right or wrong.