So when is a SUT really needed?

@lewm 

"I described my interpretation of RB's statement about the damping effect.  RB did not explain the phenomenon; he only mentioned it.  Based on my definition of a "diatribe", I would not say that my post contained a diatribe against anything. As to the rest of what you wrote, I don't follow you.  No matter what LOMC you are using, you have a choice regarding input impedance of the phono stage or whatever the LOMC is directly driving ahead of the phono inputs.  That choice is in addition to all the other elements that you mention.  Furthermore, I am not saying that cantilever damping as a result of current through the coils of an LOMC is good or bad; it's just an idea that has been discussed here and elsewhere.  Like I did mention, some think it is a problem while some others think it might actually benefit performance by the damping effect. Dave Slagle might want to comment; he does this stuff for a living."

It starts to look like "diatribe" when the OP is asking relatively simple questions that anyone would ask and we're trying to bring him up to speed on the only information that manufacturers and the hi fi press avail to us and you go off on tangents about advanced electrical theory which really just would confuse and create a conundrum for the poor guy.

Given the basic information available to the consumer, even a poster's most "practical knowledge" on these forums should be enough for the OP to make a rational decision about how to move forward and where his money might be best spent. Even using the most inexpensive and rudimentary tools available you can achieve precise results and spectacular sonic performance from budget or very sophisticated hi fi equipment. 

@jay73 ,

a few answers to your Q.

1. A true step up has no cord and does not plug in. Its a stand alone unit. 

2. A step up is not a step up. There are varying degrees of bandwidth and gain levels. 

3. when is it needed? depends on how low the power supply noise floor (ripple and signal to noise ratio) is on your phono stage and how much output a given cart has. The lower the output level on an MC cart, the more likely a step up will help. 

Once a person decides on a step up there are so many options from super inexpensive to outrageously expensive. 

I dove down that hole a few years ago, and could not easily return to a phono stage with no step up. 

Faustuss, I think you need to look up “diatribe”.

Policing this forum is a thankless task.

I echo what @viridian said. His statement clearly explains. 
I alone can’t do without SUT. I like how it sounds.. I tried Parasound jc3+, Sutherland 20/20, Ayre, Lab12 master, MoFi master.. simple SUT just makes my setup sing.. I have a Koetsu Urishi Wajima with Clearaudi Master reference turntable. 

"I like how it sounds."  That about sums it up.  You use a SUT with an MM phono stage for your LOMC cartridge, if you prefer that result to using your LOMC with any other amplification device, which might include a higher gain phono stage that in and of itself provides sufficient gain or an outboard active gain stage ("head amplifier"), which for the OP's benefit is a plug-in device that adds only gain, not RIAA equalization, to the output of the LOMC. The output of the head amplifier then must be fed into an MM phono stage for RIAA correction and for added gain, just as in the case of using a SUT.  In recent years (to the OP), the idea of amplifying the current (not the voltage) output of an LOMC has come into vogue among some.  So now you have the additional choices of using an outboard gain stage that operates on current gain and that then puts out voltage to drive an MM stage or a current-driven phono stage that affords lots of voltage gain at its output sufficent to drive the downstream linestage or direct to an amplifier.  It's a bit bewildering, and there is no perfect answer. You have to try a few of the alternatives for yourself and make your own decision. Moreover, one doesn't know what else you (OP) do or don't know, so please ask more questions.