Does Nest utilize all the benefits of a communicating furnace
Nope

The Nest can only control furnaces that use "on-off", 24VAC control systems, such as conventional and two stage furnaces.  Fully modulating communicating systems (such as your Lennox iComfort, or the Carrier Infinity) use proprietary serial protocols that the Nest doesn't know how to speak.

This means that in order to get the full benefits of modulating operation at this time, you need the matching system thermostat -- otherwise, your furnace is simply a rather good single or two stage furnace, not a modulating furnace.