One of the great things about working with Lightroom’s Develop module is that anything you do can always be undone.

If you want to undo everything you have done, you can click on the Import step in History:

or hit the Reset Button (in the bottom right):

Let’s look at the difference between the two methods:In my example, I want to start over, and then convert the photo to black and white.

First I do this by clicking back on Import in the History panel, and then converting to black and white:

Next, I do the same thing by hitting Reset  instead, and then converting to black and white:

They both allow me to start over with my photo, but if I use Reset,  I do not lose the history of steps I took before I hit Reset — Reset becomes a step in History.   I have the option to change my mind and go back to the work that I had done before starting over.  Starting over by clicking on Import in the History panel doesn’t preserve this option for me.

Therefore, if there is any chance that I will change my mind on undoing all my changes, I will use Reset instead of clicking on the Import step in History.  If on the other hand, that work is not important to me and I don’t want it taking up space in History, I will click on Import.

A note for those of you who work on your images on one computer, then transfer and import them into Lightroom on another computer: your Import step may not be the beginning of your work.  In this case, for you to get back to the beginning, Reset is the option you would use.