Totally confused about Sandbox

[CaptSaltyJack]

I'm pretty techie, but I'm having trouble understanding how this works. I've read the user guide, I still don't get it.

So let me get this straight, regarding the process:

1) Boot your main drive (Mac HD), and run Super Duper
2) Run the Sandbox operation in SuperDuper (shared users & apps) and it copies Mac HD to another HD called Sandbox
3) Now you boot the Sandbox volume and use that as your day-to-day drive
4) Weeks pass by, maybe months..then suddenly after a system update, your system is toast.

Now the problem is, my Mac HD system files are way way out of date. If I boot to the Mac HD, sure, the bad update that hosed me is gone, but so are the 50 other system apps and other stuff I've installed since then!

I also don't understand this, from the user's guide:

Need to update an existing Sandbox? No problem! SuperDuper’s amazing
Smart Update feature will update it in minutes. Simply boot back to the
original and follow the steps above, substituting Smart Update from
Macintosh HD to Sandbox for Erase Sandbox, then copy files from
Macintosh HD. SuperDuper will automatically check each and every file and
directory on Macintosh HD and Sandbox, copying any files added or changed
on Macintosh HD to Sandbox. Any files that are on Sandbox that aren’t on
Macintosh HD will be automatically deleted.

Huh? If I've been using the Sandbox volume for a while and ONLY the Sandbox, why would I want to boot the Mac HD and update to Sandbox? It would overwrite any non-user files I've updated.

Someone help clear this up for me. I just don't understand it. And I also don't get: why use the Sandbox as the day-to-day boot drive? Why not just dump to Sandbox, and keep using Mac HD, update to Sandbox once in a while, and when Mac HD gets toasted, boot Sandbox and update to Mac HD?