I do it sometimes. I used to do it more until people critiqued that I did it too much. Now I save it for when it seems a composition warrants it more, or to add a dynamic element. Either way I do it with more intent now and sometimes will shoot one straight and one tilted and decide which I prefer later.
One application I see fit is when the subject is leaning or has their head tilted, and you want to put the eyes on a straight plane but slant the rest.
This one I shot both straight and tilted. His head is leaning a bit, and in the end, I liked the tilted photo better. It felt like there was more connection to his face and the angled line of the chimney added some interest. This may be a matter of opinion. I’m sure some people would have preferred this straight.
This one is a fun shot of my friend. I liked the angled look of the bricks in the background.
http://www.flickr.com/photos/roxanne_elise_photography/9243528139/
This one I probably should have shot straight. In hindsight it seems like she’s going to tip over.
This one I did on purpose. They were standing on a hill too, but I thought this added some interest and a change of visual weight to their pose.
Not a portrait, but the angled lines added interest.
This was with intent. It was to create movement.
This I tilted to keep her eyes on a straight plane, but I think I might have tilted it too much. I should have found a happy medium because now his eyes are tilted.
Another where I used it to balance out the tilt of her head.
I should NOT have done it here. There is nothing to balance it out.
http://www.flickr.com/photos/roxanne_elise_photography/8052694474/
Should NOT have done it here either. My intention was a tight crop that also included the neat milk crate, but it just makes me tip my head. I have a few others similar to this that I shot straight-on and like better. (This is my friend who is also a photographer).
I used it here to emphasize motion, though I used it too much within this set. Some work and some I don’t think do.
I like it here. It was to get the rifle in the frame yet keep a close, dynamic crop.
I think it’s fun here
but does not add anything here
This was done also to balance her eyes out.
Again, I did it a lot more in my earlier work. I keep it minimal now. I think it also works better in close crops and looks a bit weird when more of the horizon/horizontal plane is visible.