The Baen CDs hosted here are freely-distributable disks provided to promote the sale of the books contained within. Baen allows these CDs to be distributed not simply to provide free electronic copies of their books, but to generate sales for those same books. They are a medium of advertising.
These CDs are generally available bound into the first edition of the books they are titled for. A few of the CDs (those marked with the P prefix) are not bound in any book and were made available as publishing industry promotional material.
Please remember that just because these books are being provided at no cost does not mean that they are in the Public Domain. Just because Baen isn't asking for any money for these copies doesn't mean that they are giving up any of their copyrights. Copyright doesn't mean that you have to pay for something, it means that someone legally owns the right to distribute something (or not) in any fashion they desire - including doing so at no charge. So all the rules that apply to an ebook you bought and paid for also apply to these titles.
If you download any of the disks, please take the time to go to the Baen Webscription site and buy a copy of at least the CD's primary ebook. For a modest investment of about $6, you can buy the book, which gives you access to a downloadable copy of the CD, anyway. Or you can buy the entire Webscription month that the CD accompanies for $15 and/or buy the book in paper form.
For more freely downloadable Baen books, visit the Baen Free Library.