thoughtbot/guides — pull request #111 by croaky (2013-07-30 23:35:53+00:00)
Title: Don't use instance variables in partials

* It is hard to reason about the source of instance variables in
partials because the source is too far away.
* Like globals, they're not given to you by your caller, and
maybe not even your caller's caller.
* That makes it hard to figure out what you're changing when you change the
instance variable.
* It couples the partial to the place it's first used.
* If you use locals, then you can follow the chain all the way back.

Thanks to @gabebw, @calebthompson, and @pbrisbin.