To really oversimplify things cocoa nib (what's left after roasting, cracking, and winnowing need to be:
a) Ground
b) Refined
c) Conched
on their way to becoming chocolate.
Nibs are ground into chocolate liquor and there are no other ingredients added. The result is a coarse, often gritty paste with a wide particle-size distribution with particles often in the 60-120 micron range, but this can vary widely.
The liquor then gets refined down to a point where the particle size distribution is in the 12-20 range. During refining other ingredients are added - sugar, milk, and vanilla. If you are using any form of crystalline sweetener you are going to need to refine it before conching.
Once the chocolate is refined, it is conched. Conching has both a physical component (improvement in texture) but also a flavor development component. There are two stages in conching. Dry (no added cocoa butter) and wet (after cocoa butter and/or lecithin are added).
A melanger (or melangeur) like a CocoaTown or Santha is technically being used as a "universal." Universals are called that because they handle all three stages - grinding, refining, and conching in a single device.
Devices like the CocoaTown were not developed for making chocolate originally. They were made for grinding soaked beans, such as lentils, into pastes. That's why they are called wet grinders. They look a lot like old-style melanguers and so they were adapted for that purpose.
You don't have to use the wet grinders as universals. You can pre-grind the nib and sugar to reduce the amount of time required to mix and refine them together in the wet grinder. Likewise, you can remove the chocolate from the wet grinder when it is refined and put it into a device that is designed specifically for conching.
The CocoaTowns and Santhas are used because they are relatively inexpensive (at least to get started) and relatively easier to understand and to use. They are not used because they are the best, or even good, ways to make chocolate. It is possible to get "real" universals of about the same capacity as a CocoaTown 65 for about the same price that will be able to go from nib to finished chocolate in under 24 hours.
It is (now) possible to buy a conche that will do in 2-4 hours what it takes a CocoaTown 65 48 hours or more to perform. The price is about 50% higher than a CocoaTown 65 for roughly the same capacity.
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