It's in the note here (before section 1.1) --> http://guides.rubyonrails.org/asset_pipeline.html#what-is-the-asset-pipeline-questionmark

I was thinking that this is essentially an override for sass-rails, so if the sass-rails gem was replaced, this would need to be updated anyway. But better safe than sorry on CSS compression sounds good, I'll add it back but keep the note.