Why we only need three independent unit to describe physics? From the article below, it is said that we can describe physics with only 3 independent units: length, mass, and time in cgs system/ velocity, action, and energy in natural units system. However, why on Earth we only need 3 independent units? why not 2,4,or 5 independent basis?  Does it had fundamental meaning in physics?
Natural Units and the Scales of Fundamental Physics
 A: See what happens to the Coulomb, according to the paper:

However, the need for an independent unit for electric charge went
  away when the dynamical laws of electrostatics were worked out.

This may be it. 
Physics is ultimately concerned with dynamical laws, because those are the laws that relate to our actual physical experience, scientifically calibrated into "experiments". We experience everything in spacetime, and what is spacetime ? Space, time and curvature, according to General Relativity. These are the MKS/cgs units. 
If this interpretation makes sense, then what it means is that there are 3 dimensions to our actual experience of the physical world, which are the defining dimensions of spacetime itself.
Now what about Natural Units? They allow us to describe spacetime dynamically, so to say. Velocity is the articulation of space and time, action governs the paths chosen by physical systems, and energy is both an expression of time considered as a symmetry and a more fluid curvature agent. All units there have an active nature, where in the cgs system we have the static blockworld units.
Now is that deep, or trivial? Poetic, at least. 
