It works in the sense that it does add an extra "reminder" and requires specific intent. I mean, in this scenario all the people already have been informed that they're absolutely not allowed to do things like that, but if someone has forgotten that, or simply is careless and just wants to "try something out" then if it's unblocked they might actually do it, but if they need to work around a restriction, that forces them to acknowledge that there is a restriction and they shouldn't try to work around it even if they can.

The smart ones don’t paste in all their private data.

And yes, if the bypassing the block is combined with disciplinary action, it does work. It’s not worth getting fired over. This is likely what heavily regulated industries like financial services and defense are doing.

Blocks are effective reminders of policies.

I remember someone trying to look up winning lottery numbers at work. The site came up "Blocked: Gambling". It was a little reminder that they're watching our web browsing at work..

Those are pre-configured firewall rules. These firewalls can go deep packet inspection and block traffic.

It's a fairly standard practice. I wouldn't associate it with overreaching surveillance.

Well, a firewall rule based on a cloud-populated access control list interrupted traffic. More likely vendor-related than employer-related.