For example my STB is on a VLAN that has WAN access (otherwise it won't do anything), but that makes it untrustworthy so it is completely isolated from rest of LAN.
On the other hand some "smart"/IoT devices are on a VLAN that has no WAN access so that they can't phone home, become a botnet, or download firmware updates that remove functionality in favor of subscription services. Only a VM running homeassistant can talk to them.
This will work until amazon sidewalk / built-in LTE modems become too frequent, at that point I'll have to start ripping out the radio modules from things I buy.