What are the strengths of chalk paint?
My experience is with the commercial brands (my wife uses and sells them).  The two main advantages that I see are:


that they allow a very smooth finish with a brush.  If you were to paint furniture with latex paint, you'd get a lot more brush strokes than with chalk paint.
it's easy to do the shabby chic thing (distressing, ageing, etc) with chalk paint.


Disadvantages:


It's damned expensive, compared to regular latex paint.
You can't color match like you can with regular paint (where the paint guy scans a color sample and the computer matches it)
It's not a durable surface at all. For furniture and such it has to be sealed or waxed, which is another step.