SSL Alpha Channel insert summing question.

[PDP]

My SSL alpha channel has a switch that sums the send and return of whatever is inserted into the channel. I have a compressor inserted on the send and return. I'm not quite sure whats happening when I select to sum(mix) the send and return. Does that mean half the signal is compressed and the other half is direct? Is there any technique that this is commonly known for in recording?

Thanks,
Pete