[GrinningFool]

> Hmm -- most migrations don't need to be reversed,

This is true - but when something does break unexpectedly in a production migration, the last thing you want to do is figure out how to do your revert/'down' on the fly.

[awinter-py]

Okay, but are you testing every 'down' command on your prod DB? Large untested operations in prod may not be the best answer in an emergency.