Removing Additional Settings Added After Migration

I'd strongly suggest to go through the release notes to understand the behavioural changes, functionality changes etc. These will help one decide what to see new on the boxes when one upgrades. 

I personally feel, no one will be able to justify what is expected as the code changes/fixes would be many considering you have made a big software upgrade from v12 to v17. 

You are required to manually find this out, referring the release notes. As long as the default configurations don't affect your Infra, which I take is the case, you should be fine leaving the default settings that got added up in v17.