For tree leaves in XML, when is it better to use attributes, and when is it better to use descendant nodes?

For example, in the following XML document:

<?xml version="1.0" encoding="utf-8" ?>
<savedGame>
  <links>
    <link rootTagName="zombies" packageName="zombie" />
    <link rootTagName="ghosts" packageName="ghost" />
    <link rootTagName="players" packageName="player" />
    <link rootTagName="trees" packageName="tree" />
  </links>
  <locations>
    <zombies>
      <zombie>
        <positionX>41</positionX>
        <positionY>100</positionY>
      </zombie>
      <zombie>
        <positionX>55</positionX>
        <positionY>56</positionY>
      </zombie>
    </zombies>
    <ghosts>
      <ghost>
        <positionX>11</positionX>
        <positionY>90</positionY>
      </ghost>
    </ghosts>
  </locations>
</savedGame>

The <link> tag has attributes, but it could also be written as:

<link>
  <rootTagName>trees</rootTagName>
  <packageName>tree</packageName>
</link>

Similarly, the location tags could be written as:

<zombie positionX="55" positionY="56" />

instead of:

  <zombie>
    <positionX>55</positionX>
    <positionY>56</positionY>
  </zombie>

What reasons are there to prefer one over the other? Is it just a stylistic issue? Any performance considerations?