The value-add is having a workstation that's disconnected from work that would be susceptible to traditional vectors that endpoints are vulnerable to. For example, building software that pulls in potentially malicious dependencies, installing non-essential software, etc. The "SRE laptop" would only have a browser and the official CLI tools from confirmed good cloud and infrastructure vendors, e.g. gcloud, terraform.
I think that such a posture would only be possible in a mature company where concerns are already separated to the point where only a handful of administrators have actual SSO or username/passphrase access to important resources.
It's not a joke. Supply chain attacks are a thing, but Google Chromebooks are about the most trustable consumer machine you can run custom code on short of a custom app on an iPad. The Chromebook would only ever have access to get the root AWS (or whatever) credentials to delete, say, the load balancer for the entire SaaS company's API/website. If my main laptop gets hacked somehow, the attacker can't get access to the root AWS credentials because the main laptop doesn't have them. The second laptop would only be used sparingly, but it would have access to those root credentials.
