Bonsai means: "Plant in a tray".₁
Bonsai is the art or process of making small trees. As a practice it came from China over a thousand years ago. The art found its way into Japanese hands between 1185-1333 and has flourished from there to monks, Japanese aristocracy, then to the general public developing into a fine art and important cultural and philosophical endeavor.
Once Japan opened its doors of isolation to the rest of the world in the 19th century, people began to take notice of this amazing and age-old art form.
"…exhibitions in London, Vienna and Paris in the latter part of the century - especially the Paris World Exhibition in 1900 opened the world's eyes up to bonsai." ₂

Because not only is it aesthetically pleasing, it's extremely functional.

• Bonsai-techniques will keep your plant small, yet productive.
  From a bonsai mum point of view, this technique comes in handy if you want to keep a small mum but also need to be able to take many cuttings at once.

• Bonsai-techniques will keep your plant "stealthy"
  A proper bonsai will only take up about a foot in height, perhaps a foot in span. Compared to larger more unwieldy mothers for cuts and strain selection, this is an option that starts to look good to the canna-farmer who has been forced to maintain smaller and stealthier gardens.
  
  The canopy over time will produce many smaller leaves using many more small branches. The finite resources of light and space will force the plant to produce small in size but maintain productivity in volume of branches and cuttings.

Bonsai farming requires less light, less feeding and less space. Pruning both above the soil-line (grow tips) and below (root trimming) will be necessary as maintenance. Familiarity with training/bending methods is useful too, for shaping the canopy, though it isn't absolutely necessary for all strains.

For the purposes of this FAQ we recommend soil or soil-less mix like Promix, Coco, etc. The reason is we're not looking for heavy, quick growth - we're looking to slow down the process of growth over time. Hydroponic and aeroponic solutions may be too productive for this method, requiring a lot more maintenance than a soil or soil-less mix would; it would require much more maintenance.

You can always speed up production of cuttings by increasing light levels and feed in the soil plants.

Somewhat, yes. Certain strains are easier and/or look better but we haven't come across one that you can't bonsai yet.

The trickiest plants to bonsai are strains that like to grow single cola and don't branch out much. Even those with regular toping will put out side shoots, they just tend to take longer to do so.

• Autoflowering strains:
  Auto-flowering strains are somewhat trickier to bonsai. Greater care is needed in pruning the top and roots. Waiting until the roots fill the pot and the plant tells you it's roots need a trim. You should do it preemptively. I've also found that a more vigorous pruning of the top is needed.
  For example: I have the sweet pink grapefruit clone (the one that went into making sweet tooth). Now it tends to auto-flower but it's possible to keep her in a full vegetative state. But you have to be vigilant, the second she stresses out a little she starts spouting pre-flowers galore. So by cutting her back and making sure she doesn't get root bound is the key to keeping her in vegetation-mode.

• Stretchier strains:
  As for plants that grow stretchy both tying down and topping is needed. In the beginning you top more forcing the plant to put out more side branches (do this a few times) then tying down to open up the plant more seems to work well.