It's a very interesting and important question.
It brings up the entire (potentially uncomfortable) question of "tagging for profit" vs. "tagging to facilitate content discovery."
If I write a post about "The science of brain chemistry," tagging both VYB and STEM might be totally appropriate and have nothing to do with trying to milk rewards. However, if the post were about "cooking a pizza," then it becomes tag spam.
Which ultimately leads to one of the issues I often railed on about, even back on the "old" chain: Automation/bots are "stupid" in a social web context because they can't actual interpret what they find, they can only make a "yes/no" decision.
As related to this particular discussion, building a community requires actual human beings (or cats!) who are willing to actually read and engage, rather than just "token farm." But beyond that VYB/POB are general content communities, meaning that there definitely are situations where tags other than our "home" tags are appropriate to use.
=^..^=