Benefits: they're light, compact, cheap, and come in several delightful colors. Disadvantages: I suppose they could rip easily, but I haven't had issues with that so far.
A graduate school professor once advised that writing is key to developing, understanding, and retaining thoughts. I've found that if I'm not writing daily, many things I learn are forgotten. And it's cool when writing produces new new ideas.
I guess this is a little plug for writing, but mostly a thanks for those notebooks at Grandmas.