What Is This Equipment For?

The current Sound on Sound has a review of Greiner Engineering Tools sum.mation.  There are frequently articles about similar summing amps and analog "mixers" (that do not actually have faders or other such mixer controls).
 
No doubt these things are great, but I don't understand where they fit in?  If a project studio has a computer running a DAW and an interface for getting audio in and out of the computer—in my case, I have both a Roland VS-700 and a MOTU—what does one do with such gear as this?
 
Sorry to be dumb, but I honestly don't understand where it goes in the signal flow—unless it is simply a better type of audio interface.
 
Thanks.

Mr. Anderton, I am a fan of writing that is clear, correct, and concise, and your answer certainly fits into that category. Thanks.

The Summation is not just another analog line mixer, or summing mixer.  Summing mixers (summers?) allegedly accomplish several different purposes.  The first is bypassing digital mixing.  Many are not sold on this aspect, tho I have to admit it is harder for me to get a mix loud on digital than analog.  Pushing digital up to -1 dB or so seems to strain the sound.  Note that I don't use a summer, so I haven't done anything scientific.  But on a analog console ...  However, some people think analog summing does the same thing.  It is a matter of taste, but I've never read that a clean summer doesn't null to a digital mix.  Which brings up another aspect of summing - those that output mic levels and need a mic preamp.  Obviously, a mic preamp has a small but usually discernable effect on the sound.  You choose your own back end that fits your ears.  One of the obvious roles of an analog summer is to attach various analog outboard to your tracks or stems.  A lot of pro mixers do this, which makes working at home viable instead of a big studio (tho they all complain about the business mode; ie. declining budgets).  If you have a few favorite bits of gear - EQs, comps/limiters, etc - you can use them at mixdown.  If you spent a couple of thousand dollars a pop, it makes sense.  The UA 6176 is about as universal as you can get for recording bass - so you mix back through it too.  double your pleasure and analog goodness.
 
Those are all reasons for analog summing.  The Summation, however, goes one step farther, since it has VCA automation for each channel.  Instead of using the DAW to control volume, you use the Summation.  this allows you to change the volume AFTER the signal hits the analog hardware.  So you keep the natural gain structure and saturation/distortion and effect of your analog hardware and then adjust the volume afterwards.  Otherwise, all those little vol envelopes in the DAW effect how hard you hit the analog hardware.  I'd love to give it a try.
 
All this is rather subtle, tho.  You have to have speakers, room and ears to use these small variations.  It won't make you sound like a pro, but it can help smooth out your sound after you get the basics of mixing down.
 
@