That’s right. I had fogotten about that. I thought about it months ago when I was debating on using SE out on my DAC to drop the voltage and hopefully reduce the gain. But I still haven’t tried it yet.
From the Head-Fi thread:
"The Platinum uses two differential amps, one per channel. The Balanced is, obviously, taken between the two outputs of each amp. The SE, however, is taken from one output of each amp to ground. This means that SE can only output 1/4 the power into the same load. This is shown in the specs on MP website.
Human hearing, being logarithmic, doesn’t really notice the power difference that much, especially when listening power is usually quite low and you can always change the volume setting. But I think the Bal out is a hair more dynamic than SE. And I have a general philosophy that a balanced amp should be run fully balanced in and out to get the best. Though this last idea is more of a personal thing than something measured out in detail.
At one point a while back I almost decided to remove the SE jacks from any future Balanced amp that i would make. A little extreme, I know, and others talked me out of it. 
If you use the Platinum SE I think you’ll be very happy with what it’s doing. It sounds great. I just think Bal out adds just a tad more to the experience. Subtle but hearable if you really try.
Input doesn’t matter. The amp should perform the same regardless of Bal or RCA ins. The RCA in has a built-in splitter so that the lower level SE signal is doubled to be more consistent with the Bal input. I have a DAC where the Bal out outputs twice the amplitude of SE. When using the Carbon (with a similar arrangement) I can live swap from one input to the other and I, honestly, can’t even tell that the switch has occurred.
Oh. One interesting thing. With the Carbons there were quite a few questions about not being able to switch the output from Bal to SE and back using the input switch. So, just to maybe anticipate one or two of these, the button on the right only swaps the input selection. Both output jacks are live all the time."
This was written by the man himself, Dr. Cavalli.
So yeah, my advice is to get the Liquid Platinum if you like the Cavalli sound. 