Summing/mixing - why inverting or non-inverting

[Aentons]

In a summing amplifier, it seems that most of what i've seen uses an inverting opamp configuration, but sometimes I see one that is non-inverting such as the ROG Splitter-Blend. I understand that the non-inverting "virtual earth" eliminates source interaction. Is there interaction with a non-inverting config? Just curious why or in what circumstances you would use one over the other?

Thanks