When wouldn't you want to remove an unused column from a database table?

This came up in conversation yesterday when columns that existed in production got the axe in lower environments demanding a triage to update production. I think this was the right thing to do in spite of the pain point of the drama. Back when I was at FramesDirect I went to one of those goofy Agile events that Java people in Austin went to because there wasn't really a Java meetup group and we all sat at a large table and told horror stories and some of the guys with AT&T had a database that everyone interacted with over one common connection string with the same username and password for everyone (no records of who used what) that had existed untouched for years. They were afraid of their database because they didn't know what all (forgive the Texas) was using it. In that scenario I might not remove a column that seemed unused. I can't think of another circumstance.