Mass email: targetlist can be set in campaign and mass email as well - why?

[qpoint]

After some testing, I think the behavior is:
They are not added/combined.
Campaign Target Lists: only used as the default when creating a new MassEmail manually.
Mass Email Target Lists: can be whatever you want. You can remove the defaults and set to whatever Target List(s) you have.
Creating MassEmail via Api: there is no presumed default from the Campaign, you must specify the targetListsIds field.

[qpoint]

I have the same question, found this post while searching. It is not clear what the relationship is between the TargetLists allowed at the Campaign level, and a separate set of lists that can be specified at the MassEmail level.

Are the lists combined? For example, if 2 TargetLists are defined at the Campaign level, and none on an added MassEmail (attached to this Campaign), will the MassEmail list of contacts reflect the 2 TargetLists?

[agri]

[EspoCRM Version 7.0.9]

I understand, to create a mass email, I have to create a campaign first. In campaign, I can set one or more targetlists.
I now create a mass email. There again I can choose one or more targetlists - even different from those set in campaign.

I doubt, which one will count. Is it necessary, to set both?

Regards