Behavior of salesforce integration for zoom webinar

There is not a lot of documentation about the actual behavior of the 3 settings under Zoom webinar settings in the native salesforce app:

Create Campaign for each Webinar: this is fine I guess, but how are fields mapped?
Add registrants as Campaign Members: what is the field mapping? It is smart enough to reference a Lead or Contact as the campaign member?
Create new Lead : if the registrant is an existing contact in the org? what if there is a duplicate?

I need to understand the behavior more before I can fully test the integration and decide if its usable for our use case

what if I only want webinar features? the full installation takes up 6 custom fields on the Activity object which is a lot for most orgs since 100 is the limit