Confused about dist-upgrade

[Bob Bernstein <poobah@ruptured-duck.com>]

A thread about dist-upgrade has me confused. In my experience 
I have only ever run 'apt-get dist-upgrade' when I wanted to move 
from one release to the next, say, from squeeze to wheezy.

Similarly, if I wanted to insure I had the latest versions of 
packages already installed (and any/all security fixes) I have run 
'apt-get update' followed immediately by 'apt-get upgrade.'

But the thread currently underway about dist-upgrade suggests that 
users are running it rather routinely, and not at all necessarily 
to move from one release to the next.

Can someone please point out what I am missing?

Thanks,

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