It does have its advantages.
You can add some smarts to the ATmega in order to simply communication.
Make your own LCD API that can do animations and stuff without loading the cpu time of the main micro. etc.
Not that a 2 line text lcd is cpu intensive, but it's a really good learning experience to do micro <-> micro communications and write your own protocols
A lot of new hobbies tend to stick to a single micro and just play around with adding hardware to it.
hehe, you're not a real microcontroller programmer until you've got multiple micros talking to each other