When I click to render an image it auto saves it somewhere at the output file and ask for replace it.

More often than not when i hit render i tend to forget that the image don't go to the output that I selected and eventually forget or lost that render, my solution is to have a temp folder that hold your render somewhere and it can store like 3 renders and then it substitute it for newer ones.

This would help not only for beginers like me but also you can be able to make a A and B comparison at the render viewer.