by Julieanne Kost
Selecting “Clear History” from the History Panel’s fly-out menu clears the panel, but you can still choose Edit > Undo Clear History. Option (Mac) / Alt (Win) + “Clear History” from the History Panel’s fly-out menu will delete the history without the option to “undo” (as if you have closed the file and reopened it). This can be helpful to free up disk space or to release RAM (or when you just don’t want anyone to see what magic you’ve applied to an image)!
In the History panel, you can also Option (Mac) / Alt (Win) -click any history state (except for the current) in order to duplicate that state. This would be a way to save a state from “rolling off” the history panel (if you have the “Allow Non -Linear History option checked on in the History Options accessed via the panel’s fly out), but I think I would prefer to save a snapshot or do a save-as if I am that concerned about loosing that point in time.