Snapshots can't cause over-provisioning, not for file systems. If I mutate my data and keep snapshots forever, eventually my pool will run out of free space. But that's not a problem of over-provisioning, that's just running out of space.
With ZFS, if I take a snapshot and then delete 10GB of data my file system will appear to have shrunk by 10GB. If I compare the output of df before and after deleting the data, df will tell me that "size" and "used" have decreased by 10GB while "available" remained constant. Once the snapshot is deleted that 10GB will be made available again and the "size" and "available" columns in df will increase. It avoids over-provisioning by never promising more available space than it can guarantee you're able to write.
I think you're trying to relate ZFS too much to how LVM works, where LVM is just a volume manager that exposes virtual devices. The analogue to thin provisioned LVM volumes is thin-provisioned zvols, not regular ZFS file systems. I can choose to use ZFS in place of LVM as a volume manager with XFS as my file system. Over-provisioned zvols+XFS will have functionally equivalent problems as over-provisioned LVM+XFS.
With ZFS, if I take a snapshot and then delete 10GB of data my file system will appear to have shrunk by 10GB. If I compare the output of df before and after deleting the data, df will tell me that "size" and "used" have decreased by 10GB while "available" remained constant. Once the snapshot is deleted that 10GB will be made available again and the "size" and "available" columns in df will increase. It avoids over-provisioning by never promising more available space than it can guarantee you're able to write.
I think you're trying to relate ZFS too much to how LVM works, where LVM is just a volume manager that exposes virtual devices. The analogue to thin provisioned LVM volumes is thin-provisioned zvols, not regular ZFS file systems. I can choose to use ZFS in place of LVM as a volume manager with XFS as my file system. Over-provisioned zvols+XFS will have functionally equivalent problems as over-provisioned LVM+XFS.