Have you ever eagerly downloaded an e-book only to find that it's a hideously formatted mess that irritates you at every page turn? Of course you have (especially if you favor free or cheap e-books). This video explains why those insults to typesetting occur.
The problem boils down to the choice of algorithm that's used to render the text. While fancy software exists to typeset beautifully, your Kindle favors a lazy layout instead, because it uses something far more efficient in order to save resources. In other words, a Kindle's typesetting is kind to its battery—but not, necessarily, your eyes. [Computerphile]