We all make mistakes, unfortunately life doesn’t have an undo button, but don’t worry Photoshop does, so at least when it comes to images you can go back and change your mind. This can be particularly useful if you are working on a complicated image and just want to try out an effect, sequence or other change without necessarily committing to it for your final version. History isn’t just about repeatedly clicking undo and redo though, Photoshop is capable of much more powerful use of historical change data than many other applications.
As a default, you settings will remember 20 actions, meaning you can rewind your image back through the last 20 changes you made. You can increase or decrease the number of historical changes Photoshop remembers by selecting Edit, Preferences, Performance and changing the History States parameter, anything from 1 to 1000 is permitted.
If your computer can handle it, having 1000 history states is great but be aware it could slow things down for you if you have an older machine. As this history information is recorded as metadata embedded within your Photoshop image file, remember each time you increase the number of history steps it remembers, you are increasing the file size and putting greater strain on your processor and memory. So conversely if your computer is struggling to cope with something you are doing in Photoshop and you can bear to lose it, try selecting Edit, Purge, Histories to free up some of that space.