(correct me if im wrong)
i think its if your motor is say a 10t and your ESC as a 12t limit then you will need to get a new ESC to use the 10t motor without killing your 12t ESC
not sure about the settings though, on my tt01 right now im using a standard 26t can and ESC but ive had my friends 19t accosiated motor run on it fine without it over heating/cutting out, ran fine just drained the battery pack twice as fast