Anyone using any of those sprite generators out there?

I just started to play with them, cause I have to change the sprite of a site that I made and thought if these generators would help.

But from 2 of the sites that I tried, it seems like they only help take 2 images, eg: a "off" and a "on" state and put them together. comes with a css to offset the height.

Is that generally how a generator works? Cause I don't think its very useful when I can just combine the 2 images myself with PS.

Just to add, I think it'll be useful if we could define the different sections along the image that needs an hover effect. Basically just to save from calculating the width to offset during the hover.