I've done both.
Switching to dedicated lpar for hosting disk and stuff.
Mainly because "if" there is some software reason that I have to reboot
"hosting" lpar I don't want to lose all my guests. Not that this happens
Our situation was that we had a lpar that I almost made the host. However
I had permission to IPL it on a whim. It was a test lpar. Hosting other
lpars would have put a big crimp in my style. While it was a PITA to
unload/reload to switch around it was the best long term decision.
Here's an example. Suppose you ran Domino on your host. And you wanted
the latest and greatest version of Domino. Which requires a somewhat
current version of the OS. If you were behind on OS that could be an
Or, you were like us, you were still running Sametime 8.5.3. You were
reluctant to upgrade to Sametime 9 on IBM i until IBM could find at least
one customer running Sametime 9 on IBM i who is willing to talk about it
(still waiting...). Old Sametime does not support IBM i 7.2. Some
versions of Domino do not support 7.2.