<p>You don’t have to decide <em>now</em> precisely what you want to do, but you should decide <em>before you begin planning for graduate school</em> precisely what you want to do with those degrees.</p>
<p>A JD/PhD is useful if you want to be a professor in a law school, although a JD suffices.
A JD/MA can be useful in some policy circles, although either a JD or an MA suffices (and the MA is a lot cheaper).</p>
<p>In no circumstance would you use a JD/PhD/MBA.</p>