Dual goal: 1. accelerate access to my repository (as opposed to often slow Internet), 2. as well as keep local backup.
In detail : It can take many many (5+) hours to install Workstation class Debian system with lots of packages from the Internet as opposed to half a hour from local media. (Blue Ray) And I have lots of PCs and VMs. And I reinstall often on my VMs, with different configurations. One-time painful step of preparing a BD XL image will pay in spades. Plus for historical and archive reasons I prefer to have a hard copy (including binary and sources). I like ancient Linux systems too, and I have a copy of remastered Red Hat Linux 9 from year 2003 (i386) plus source on DVD, which is useful for educational reasons. Definitely worth an M-Disc. A decade or two from now, Debian Linux 8 may also become an education curiousity, like the classic Red Hat Linux 9 is today. Regards, -Alexey "Technologov"
