Where should I manage the user groups during the Migration?

I have to migrate users from target to source domain,

Once I start the migration, there will be users in both source and target domains.

As I migrate users to Target, I will disable them on Source Domain.

My question is:

During this migration, where do I manage the user groups, on Source or on Target Domain?

Should I wait until all the users have been migrated to start migrating user groups?

Thank you,