@weaverryan - what I am saying is it **does not** makes sense here. Triggering of GC is nothing to do with this feature so the caveat must not appear here or it is both confusing and in the wrong place meaning people would not see it unless browsing this particular entry. 

If there is any place for a note (and I would say note not warning), it would be here: https://github.com/symfony/symfony-docs/blob/master/components/http_foundation/session_configuration.rst#configuring-garbage-collection