With O365 groups and now Microsoft teams, their creation creates a SharePoint site associated with a group or team. Although these sites are site collections in the /sites/ namespace, they are hidden from the tenant SharePoint admin site hierarchy area. How do you list, manage and control these SharePoint sites? How do you distinguish between sites created through the admin area versus sites created by a group or a team?
You can get a list of all sites created by teams or groups by navigating to the root SharePoint dashboard from the App launcher and adding this search string:
This will show all sites and sub-sites in the site collection including ones created by groups or teams under the /sites/ namespace.
Turning off the ability for users to create their own sites
In the O365 SharePoint admin center settings, set Site Creation and Subsite Creation to "Hide"