Quite right, it’s the lisp reader which constructs these values. Hence the object is constructed (once) in the read phase, and may be manipulated (perhaps repeatedly) in the evaluation phase.
Here are a couple of Q&As on the subject:
‘C-h f quote’ is quite explicit on the point, if you remember to look at that.
The documentation on ’#s’ is considerably less clear, OTOH, so there’s a recent bug report about clarifying the subject in general: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23417
– Anonymous 2016-05-23 09:26 UTC
Just to clarify, the warning is not about not using, it’s about using. The advice is not to use them, have I understood correctly?
– erez 2016-05-23 12:33 UTC