Fallout 4 has a creative bent to it already, with its systems specifically dedicated towards not only the gathering and allocating of resources, but the construction and customization of entire settlements.
Automatron expands the toolset at your disposal in one major way: you can now build robotic companions.
How do you build them? Well, much in the same way that you build other things: at a specific workbench, with components gathered elsewhere. Now you can harvest parts from other robot types for use in constructing your own implements of death and destruction. Enemy Protectrons, Assaultrons, Mister Handys, Sentry Bots, and Robobrains (the Mechanist's specialty) are ripe with parts that can be looted and retrofitted to fit your new Automatrons.