Stackoverflow uses a lot of "sub-tags" as I call them, for example c#-4.0 that help add value to the question by letting you search for specific information that wouldn't really work as a combination of tags (does anyone really want a 4.0 tag?!?!). These are basically tags that are a more specific version of a general tag.
Things are similar on this site. For example, dominion-openings probably shouldn't exist as there is already a dominion and openings tag, and this would merely be the intersection of the two, as would be c#-polymorphism on Stackoverflow. (sorry for the Stackoverflow example for those who don't frequent there as well, but it helps to illustrate the situation).
But what about tags that apply to specific aspects of specific games? I just retagged several questions to mtg-manabase as it would likely be difficult to find these questions without a tag and a manabase tag would apply only to magic anyway. We have already chosen to use "sub-tags" for expansions, like dominion-seaside. What sub-tags should we encourage/discourage? Would chess-sacrifices, stratego-placement, go-defence, or bridge-bidding be allowed, or should these be organized in some other way (I tried to find some edge-cases)?