I think I figured out how to control it.
When it pops up, close it. Then either save over your current current workspace, or save a new workspace. Then it should not appear anymore, until you ask it to. (I'm still not sure exactly how manage workspace settings. Sometimes it seems like any shift you make to your palette arrangement gets automatically saved to whatever current workspace you have selected – but then that would mean closing one of the palettes, the CC libraries for example, should also update the current workspace, and not show up. I don't know, at least for now the issue seems to be fixed).
The most common reason for having the Library panel pop open are some unfortunate default settings in the current version of InDesign. But they can be changed.
Open the Swatches panel, and choose New Color Swatch. Uncheck Add to CC Library. Open the Paragraph Styles and Character Styles panels. From the panel menu(s), choose New Paragraph Style or New Character Style. Similarly, Uncheck Add to CC Library.
These are sticky settings and you probably won't be bothered.
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If you are using the workspace called Essentials and you reset it, the CC Libraries panel will open.
If you switch to Advanced and reset it, the CC Libraries will remain closed. It is also closed with some of the other preset workspaces.
And you can create your own New Workspace where the dreaded panel does not even exist!
(Not a big deal, but they have been called panels ever since Adobe bought Macromedia.)
In addition, be sure to follow what Steve said.
Great idea, Fraser!