Asa H frequently uses multiple microcontrollers in order to control various parts of its robot body. (See, for example, my blog of 14 December 2015 where Lego NXT brain bricks were used.) As a possible lower cost substitute I have bought and will evaluate one of the adafruit boards.
The multi-microcontroller architecture makes it easier to add additional functionality over time. (See, for example, H. W. Lee's MSc thesis from Cornell University, May 2008.)