Rails bundle install production only

I'm still new to rails/ruby/bundler and am a little confused. In our config/application.rb file there's this bundler segment: if defined?(Bundler) # If you precompile assets before deploying to production, use this line Bundler.require(*Rails.groups(:assets => %w(development test))) # If you want your assets lazily compiled in production, use this line # Bundler.require(:default, :assets, Rails.en