an alert is just a different format of text that only admins can use. pretty much its bold and red so that ppl can read what an admin says better, and for members to know that the warning is coming from an admin and can be backed by a ban.
I used alerts several times when I first set up the mailing system, but then blogs came along, and I'd just post a blog then put it on the homepage. Now that the websites are being divided into sections, I figured that the alert system is, once again, the easiest way to quickly see that something new is available concerning the websites.