So I'm testing with Group Account Migration in the ADMT 3.2. 

When you get to the screen that has "Copy group members" on it, what exactly does that mean?
Does it mean, migrate the group to the destination domain/OU, as well as all of its members to the same destination? 

In the Help/Description, it says "If you do not select this option, ADMT creates the group in the target domain, but the group does not contain members". 
I'm confused as to what that means. Does it mean the Group will no longer contain members so after the migration, you have to re-add all its members?

What's strange is I migrated a Security Group between two domains. It was a test group, and it had 3 test account members.
I didn't check this box, and after the migration, the Security Group was indeed in the new domain, but it still contained the same members that exist in the parent domain.
According to my understanding of the description, since the checkbox isn't checked, the test Security Group I migrated should have had no members in it after the migration.

The link below is to microsofts guidance on ADMT 3.2

http://www.microsoft.com/en-us/download/details.aspx?id=19188

The link below is to microsofts guidance on ADMT 3.2

http://www.microsoft.com/en-us/download/details.aspx?id=19188

So I guess the "Copy group members" is for Global Groups, not Universal Groups? 

Are you using the new ADMT 3.2?

http://connect.microsoft.com/site1164/content/content.aspx?ContentID=30561&IsDraft=False

Hi,

Thanks for your post.

As far as I know, this option Copy group members will try to copy all the users in the group as well, which we will do later. So we won't select.

And because global groups only contain members from their own domain, they cannot be migrated from one domain to another. ADMT changes global groups to universal groups when they are migrated.

Please read the following articles about group migration 

https://technet.microsoft.com/en-us/library/Cc756073%28v=WS.10%29.aspx?f=255&MSPPError=-2147217396

https://blog.thesysadmins.co.uk/admt-series-7-group-account-migration-wizard.html

Best Regards,

Mary Dong