Gemfile, the asset pipeline: Why have the group :assets in your Gemfile?

[David Zhang]

Heroku, as shown here - http://devcenter.heroku.com/articles/rails31_heroku_cedar - shows a Gemfile in which the following exists:

# Asset template engines

group :assets do

  gem 'sass-rails', "~> 3.1.0.rc"

  gem 'coffee-script'

  gem 'uglifier'

end

I don't understand why these gems are grouped.  Why not omit the group :assets do ... end? What does this do, exactly?

I'm asking because something really peculiar happened: I get the "Sass Syntax Error: File to import not found or unreadable..." when the imports definitely should work. When I remove the group :assets, run "bundle install", and then check rails server, the imports work fine again. And here's the oddest of all: when I revert my Gemfile back to having the group :assets as above, and then run rails server - the imports still work although my Gemfile was back to what it was when the imports didn't work. Thoughts appreciated.

(Btw, I use Rails 3.1rc4, and I'm trying to deploy to Heroku asap)

[NARKOZ]

You don't need this gems in production