Using the 'draw' image function, we ran into some problems (using ODK collect). Respondents make a drawing, save it, but later notice that they made a mistake. For example they misunderstood the question and drew the wrong thing. However, they cannot erase the saved picture anymore. Resetting only restores the previously made sketch.
I see how intermediate saving and resetting to the initial drawing can also be useful in the absence of ctrl + z ;), however it would also be nice to have an eraser!
To me that does not seem like a complicated addition to develop for this feature.