I mean, would you want it to serve clients outside of your subnet? I guess maybe if you had something like a guest network. But I tend to take the “fuck it, you get basic service and nothing else” approach to things like guest networks.

Isn’t it a potential security issue to have your pihole serve things on any subnet, because it allows an improperly configured firewall to stab at your pihole? I think you can specify any additional subnets it will serve in the settings somewhere. But IIRC, the default behavior is to intentionally drop traffic from unknown subnets. But that’s just off the top of my head.