Since UBCD is a primarily a DOS environment, as long as the hard drive is not being accessed CTRL-ALT-DEL can be used to reboot or the computer can be shut off without damage to the PC. Even those utilities that boot a Linux environment will not cause damage to UBCD since the utilities are booted from an image and not a live system.
The reason Windows and Linux machines need to be shutdown properly is that they are running multiple programs at the same time and may be accessing the HD which could cause damage to files if turned off.
I respectfully disagree. First, UBCD has not only DOS-based tools. Other tools included in UBCD are based on other OSs.
For those other tools, you can't really know what happens if you simply press <ctrl>+<alt>+<del>. It is correct that UBCD itself runs as live (or equivalent), but in most cases you are performing some action on your hardware (HDD, BIOS...). While UBCD itself won't be damaged, your hardware could.
You don't want to exit any cloning tool in the wrong way. Some cloning tools in UBCD are Linux-based and some work under a proprietary OS. You MUST follow their instructions, including to exit the program.
For any password-related tool goes the same (and users are usually not following the complete procedure and then they ask why the password was not deleted or recovered).
Any partitioning and/or formatting tool MUST be finished correctly. While "some" of those could be ended by <ctrl>+<alt>+<del> (and only when all the actions are really completed), some of them should not. The "exit" function is not "decorative".
I could mention more examples, but you got the idea.
One additional factor to consider is "electronics". While in most cases you can reboot and continue with your work, sometimes the task involves troubleshooting a system. In some cases, the RAM can remain "charged", so for some troubleshooting tasks the recommended step is to completely shutdown the system and leave it some minutes powered off, to let the RAM completely discharged.
But the opposite is also true. There are some cases where you should not power down your system, and others where you shouldn't even reset it.
So, since we are talking as a general rule, saying that you may use <ctrl>+<alt>+<del> is not correct. Sure, there are "some" cases where you could/might, and others where the program you just ran says you should, but that does not mean that pressing <ctrl>+<alt>+<del> is "always safe" or "the correct procedure" as a general rule.