What's the point of the CDU XPDR preset screen?

[MarkS]

AFAIK, you don't get to assign your own transponder codes, they're assigned to you by ATC. You don't often change the code in-flight, and even if you do, you won't know what it is until ATC assigns it. Of what use then is the transponder preset page on the CDU? I suppose you could pre-load all the 7x00 emergency codes. I feel like I'm missing a piece of information that makes this make sense.

[Sunake]

You could preset non discrete vfr codes for when you cancel IFR or are vfr and you leave controlled airspace, or even a non discrete ifr code like 2000 when you enter a non radar environment like oceanic or something