How do I Keep Control of SharePoint Site Creation?
The simple and honest truth is that by default you cannot keep site creation under control. You need to make change.
Owners are Gods!
Out of the box, users can create sub-sites within site collections that they are owners of – once they’re an owner, they’re god!
To maintain a level of control you need to think about how you are provisioning sites. Provisioning – creating something for a purpose or use – in the context of SharePoint is about control. Through the use of provisioning technologies which could be solutions built (using code, Flow, Logic Apps or workflow tools) or bought (such as ProvisionPoint) control can be maintained at the top, where it belongs.
Without the controls that provisioning solutions provide you will get sprawl; the continual creation of sites all over the place.
Provisioning solutions let you remove the privilege that an owner user has to create a site and proxy that creation through your solution. Once in place you can apply rules through your solution. Voila! Control, top down.