To add to @hpy’s great explanation. The issue with licencing is that for each type work that is being licenced there are specific considerations that go into the licences that make little sense to other works. This is particularly important in terms of how they define the terms they are using. For example the GPL v3 has sections defines terms such as:
- Source Code.
The “source code” for a work means the preferred form of the work
for making modifications to it. “Object code” means any non-source
form of a work.A “Standard Interface” means an interface that either is an official
standard defined by a recognized standards body, or, in the case of
interfaces specified for a particular programming language, one that
is widely used among developers working in that language."
And the CERN OHL S v2 has terms such as
1.3 ‘Source’ means information such as design materials or digital code which can be applied to Make or test a Product or to prepare a Product for use, Conveyance or sale, regardless of its medium or how it is expressed. It may include Notices.
1.4 ‘Covered Source’ means Source that is explicitly made available under this Licence.
1.5 ‘Product’ means any device, component, work or physical object, whether in finished or intermediate form, arising from the use, application or processing of Covered Source.
1.6 ‘Make’ means to create or configure something, whether by manufacture, assembly, compiling, loading or applying Covered Source or another Product or otherwise.
It is very unclear, how these may apply to documentation. Or in fact, how software licences may apply to hardware. If you are not a fan of Creative Commons there are other open documentation licenses, such as the GNU project have the GNU Free Documentation License, but they have their issues.
Hopefully, everyone downstream will act within the spirit of the license, making the legal issues less important. But this cannot be guaranteed, and so it is always better to use a licence appropriate to the work.
As for the creative commons licenses, the are quite tunable to your needs CC BY-SA is copyleft and somewhat philosophically the same as GPL. CC-BY is not copyleft and is more philosophically akin to permissive licenses like the MIT license. There are also Non Commercial (NC), and No Derivatives (ND) versions of the Creative Commons licenses. However, these NC and ND licences put up barriers to free use and in my opinion should be avoided without very good reason.