It's not necessary, but it's a common pattern. At a minimum, you want to be assigning the user to an instance variable, since you'll almost certainly need the user in the view.

An alternate pattern is to do something like this:

```ruby
def index
  @submissions = user.articles.order("updated_at DESC")
end

private

def user
  @user ||= User.find_by_user_name(params[:user_id])
end
helper_method :user
```