As someone who has multiple times heated up my soldering iron and realized it had the <big|small> tip on it when I needed the <small|big> tip, and then gone through the annoyance of swapping tips on a hot iron, I can think of at least one thing to do with two irons.
As someone who has multiple times heated up my soldering iron and realized it had the <big|small> tip on it when I needed the <small|big> tip, and then gone through the annoyance of swapping tips on a hot iron, I can think of at least one thing to do with two irons.