Yes, I can see the benefit of this.
Just a couple of things. I did a test page with three images (all the same one) and resized them in various ways just to see how it worked. Then in the Server behaviours panel I get three instances of the behaviour but they all say the same "Image Resizer (image_cache)" Is there a way to show which is which? A small thing really.
Secondly, I'm a bit confused over what crop from centre actually means. I had an image 250 x 226 and cropped from centre expecting it to crop out a section of the image but all it did was resize it to the new size (in this case 50 x 50). So I end up with a thumbnail of the complete image. What's the difference between that and fit to box. I'm sure it's just me being thick.
Apart from that marvellous! :)