Partial carburetor heat is the most effective use, but it does require accurate carburetor air temperature instrumentation.
The use of full carburetor heat in most light airplanes is not a function of necessity, beyond that required due to lack of instrumentation, and lack of pilot training (and experience). It becomes an all-or-nothing proposition, in which excess heat is often used, beyond that which is appropriate to put the carburetor in the ideal temperature range.
Lack of instrumentation is a function of economy, and full carburetor heat becomes a simple act of pilot-proofing the airplane, or more specifically, protecting the airplane from the pilot.