has_many :through with has_and_belongs_to_many in Rails

Question

In Rails - what is the effect of using has_many :through with has_and_belongs_to_many? Consider having two models - Posts and Tags which have a many-to-many relationship as indicated below:

class Tag < ActiveRecord::Base
  has_many :posts_tag
  has_and_belongs_to_many :posts
end

class Post < ActiveRecord::Base
  has_many :posts_tag
  has_many :tags,  :through => posts_tag
end

class PostsTag < ActiveRecord::Base
  belongs_to :tag
  belongs_to :post
end

The reason I use has_and_belongs_to_many is because a tag belongs to many posts.

I did look into the Rails Association guide and see that they don't mention this case for a many-to-many relationship. I, however, did try this and running it in Rails didn't yield any behavior and from the small test database that I built, also seemed to return the correct results for post.tags and tag.posts - where post and tag refer to an instance of the Post and Tag models respectively.

Is this correct usage or does it have any side affects that I am not aware of? Also, if it is correct, is this the Rails way of achieving this?

Thanks!