the how to build a robot tutorial is not one that say connect the battery to the input of the MCU. so there is no explicit advice on the MCU. its just a basic guidline of you need this... and you should use one of these cuz it makes your life easier. read through it again and again. Its there to help you design and aquire parts for a robot not how to build one step by step.
if you want a step by step look for the $50 line follower or similar.
like a photovore robot for $40.