Rails: Better understanding dynamic scopes

Question

This is my "dynamic" scope:

  def all_games(conditions = {})
    scope = games.includes(:stats).scoped {}
    scope = scope.where sport_position_id: conditions[:sport_position_id] unless conditions[:sport_position_id].nil?
    scope = scope.where sport_id: conditions[:sport_id] unless conditions[:sport_id].nil?
    scope = scope.where team: conditions[:team]
    scope.order(:date)
  end

The method above is in a module that is included with my User model.

So you would access this in code, like so:

u = User.find(1)
u.all_games(sport_position_id: params[:sport_position_id], sport_id: current_sport.id, team: params[:team])

When doing some Google searching for dynamic scopes, I came across Ryan Bate's RailsCast on anonymous scopes (http://railscasts.com/episodes/112-anonymous-scopes). I modified it since I am using Rails 3, but was wondering, if I was on the right path when it comes to writing dynamic scopes?

I find myself sometimes writing dynamic scopes because of the nature of some complex API's I am writing.