Why run wpaclean when its' output file isn't used?

[Kiruna]

I'm confused about the wiki page http://hashcat.net/wiki/doku.php?id=cracking_wpawpa2:

wpaclean <out.cap> <in.cap>
aircrack-ng <in.cap> -J <out.hccap>

What's the point of the first step, running wpaclean, when the output file <out.cap> is never used?