Mainly because columns and table cells look awful on smaller screens when the text is set to justified. Here's an example:
I would like to split "sublocotenent" and other long words so that when they get squeezed closer to each other there won't be such huge gaps in the text. It will break at "subloco-" and continue on the next line. This probably isn't guaranteed to get rid of all the gaps (depending very much on the software's handling method, font selection, font size, etc) but I'm sure it would help, to some extent.
This is obviously intended for re-flowing formats such as tagged PDFs, ePub files. I don't know about Mobi/PRC. Will they survive a conversion? And will they be read ok by e-readers?
What am I saying... Is this even possible at all? Can it be done?