Substack vs. Library Stack

[Mike Kerner]

I have not read a straight answer on this, yet.

Library stacks vs. substacks why use one vs. the other?  I don't see any
clear advantage to Libraries, per se, even for...libraries.

-- 
On the first day, God created the heavens and the Earth
On the second day, God created the oceans.
On the third day, God put the animals on hold for a few hours,
   and did a little diving.
And God said, "This is good."