Arguably, the ATmega328P is being left behind as ‘the Arduino processor’ because Arduino’s are following the rest of the world and going 32bit.

If you're developing a wrist watch, a small light-following robot, or a portable weather station with Arduino, one of the best boards you can use is the Nano, and for good reason. It's pretty compact, ...

So you've already outgrown Arduino's most beginner-friendly board, the Uno, and are looking to move on to bigger, more exciting projects. In that case, the Nano family might just be what you need.