During the Teams Provision Task, ODM Discovers the source underlying Teams SharePoint site. If this Teams SharePoint site discovery finds more than 1 web or more than 4 lists, then the Teams SharePoint site is flagged as "Customized". The "Customized" value indicates that the Teams SharePoint site has had items added to it beyond the "default" or "out of the box" state of a typical Team.
The Standard or Customized flag will be shown in the Teams grid after the Provision task has been run:

For best performance, Teams flagged as "Standard" should be migrated with other "Standard" Teams in the same collection with the Standard (Channel Files Only) option selected. Teams flagged as "Customized" should be migrated with other "Customized" Teams in the same collection with the "Standard and Customized (All SharePoint Content). Migration takes longer." option selected.
Note: Migrating "Standard" Teams with the "Standard and Customized..." option will cause the migration to take longer than if the "Standard" migration option was selected.

The "Standard" migration option will migrate the Document Library as well as Site Assets lists. The "Customized" migration option will migrate the entire SharePoint site, which will take considerably more time and should only be performed for those Teams that are flagged as "Customized".