Or should that be with the goal of achieving nothing? That's not what I mean though, but I think you know what I mean.
If you don't want to do it in your camera, you can always do it in photoshop just be messing around with the opacity once you've put both images into the same frame. Some photographers centre their whole technique around this and create the MOST beautiful pieces. For example, look at Dan Mountford. He's super young still, I think... and clearly a genius.
And this isn't even one of his best pieces, just one of my favourites.
Photographer: Dan Mountford