Earlier quoted context omitted.
I think he means don't plug a power bar into another power bar.
Yes, that's exactly what he meant. And what I mean is that you can plug a power bar into another power bar, as long as you're reasonable about the total load you put on the circuit.
I think the danger outside of load would be rare, but IIRC US specs for power cords specifically don't require compliance with daisy chaining (similar to C undefined behaviors?) and I bet most commodity power bars are cost-optimized to all hell.
Disclaimer: I am not an electrical engineer.