What's the 'environment' task in Rake?
You can get access to your models, and in fact, your whole environment by making tasks dependent on the environment task. This lets you do things like run rake RAILS_ENV=staging db:migrate.
See "Custom Rake Tasks".
It loads in your Rails environment so you can actually use your models and what not. Otherwise, it has no idea about those things.
So if you made a task that just did puts "HI!" then you don't need to add the :environment task to the dependencies. But if you wish to do something like User.find(1) well that will need it.
Including => :environment will tell Rake to load full the application environment, giving the relevant task access to things like classes, helpers, etc. Without the :environment, you won't have access to any of those extras.
Also => :environment itself does not make available any environment-related variables, e.g. environment, @environment, RAILS_ENV, etc.