It is very common for circuits to have the same subcircuit repeated multiple times. Currently you have to cut and paste the circuit multiple times in Eeschema and then layout each instance of the subcircuit one at a time in Pcbnew. I am aware of the klonor-kicad scripts ( https://www.youtube.com/watch?v=mChTfL746Fs ) but they really don't work very well if you want to make changes to the schematic and then propagate them forward to the PCB. If had the ability to have a subcircuit automatically repeated multiple times in the schematic editor and then had the ability to copy the layout to the different instances of the circuit in Pcbnew that would be a huge time saver. It would also result in nicer looking layouts since it would get copied exactly right. For me personally this is the biggest problem I have with KiCad, which I think is generally pretty great. It is weird to me that this is not anywhere on the development roadmap.
They are called sheets in Eeschema. You can reuse them at will and copy the .sch file and use them in other projects as well. It's a common well documented technique. There are some weaknesses in the current design. The .sch file must be in the same path as the project file. I'm hoping to fix this during the next development cycle.