Routes: has_many vs. nested

hello

i was just wondering what the diference between

map.resources :posts, :has_one => :author, :has_many =>
[:comments, :trackbacks]

and

map.resources :posts do |posts|
posts.resource :author
posts.resources :comments
posts.resources :trackbacks
end

is.

which one should i use? is there a difference at all?

thanks!

gerold