There are, for one if your want to install quickly, I found that if I am
installing on multiple systems and don't really want to bring up a GUI first
(blank HD or some such) I prefer to use the Alt CD method because, well, no
GUI just goes.

If the system has very little RAM, as in, 256Mb or so, anything less than
512Mb. Mainly because the I have also found that the unionfs driver (that
allows the Live CD to boot into a fully working copy of Ubuntu) likes to
have more RAM than that and sometimes causes problems if you're working on
less than 512, though I have gotten it to work on 256 it was very slow.

Lastly, if you have some strange driver combination in your video devices or
X won't recognize your mouse (or name other needed device here) off the bat,
it can be good to get an install going then deal with the problem after it
is installed since you can always bring up a command line in Linux as long
as your keyboard is working.