Well kindlegen basically just strips all code that isn't on Amazon documentation from HTML and CSS. So if your ePub is not too complicated the results should be satisfactory. This can change when you will try convert fixed layout where hierarchy of DOM isn't logic.
To give you straight answer: It not make any difference unless your DOM is in logic order.
DOM (Document Object Model) define structure of an document. Ideally structure (or hierarchy ) should be logic in terms of rendering. For example:
<div>
<p>Lorem ipsum</p>
</div>
<div>
<p>Lorem ipsum 2</p>
</div>
here you have two divs with two paragraphs one after the other. If you will not manipulate with them, they will also render one after the other. But you could use CSS or JS to manipulate them and render <p>Lorem ipsum 2</p>
before <p>Lorem ipsum</p>
without change your actual HTML. This situation happens very often when you designing fixed-layout ePub which are parto of ePub3 spec.