If one tag is finer (more specific) than another, should a question tagged with the former also be tagged with the latter?
For example, a question about meat is pretty much always going to be about food. Likewise, a question about kashrut-kosher is pretty much always going to be about food. Should we tag such questions with food also? Should we detag them with food?
One question is whether the finer tag is really necessary. What value does a "meat" tag bring that "food" and "kashrut" don't bring? (For that matter, is "food" valuable?)
Can the info page for a fine tag include a link to the parent tag? It's not ideal because people won't always go there, but it at least provides a path.
This is another argument for naming "families" of tags with a common prefix; you're more likely to notice the parent tag if they're named, e.g., "food" and "food-meat". Conversely, when you're typing tags, if you meant to type "food" because you didn't know about the finer tags, with that naming scheme you'll probably be offered "food" and "food-meat". Without that, the general tags will collect a lot of stuff that "belongs" in the specific ones except people didn't know about the specific ones so they didn't use them.
halacha-jewish-law instead of kashrut-kosher, shabbat-sabbath, etc. There have to be finer and coarser tags — or at least finer ones.
passover-seder-hagada is finer than pesach-passover and meal-seudah, and kashrut-kosher is finer than halacha-jewish-law and food. (2) It doesn't work with synonyms. For example, if permitted-eats sees use, it will be made a synonym of (in your plan) halacha-kashrut (say), but someone typing in permitted-eats thereafter won't see halacha-kashrut-milkandmeat suggested.
meat not about kashrus include "BBQ for Yom Hatzmaut" and "Custom to refrain from eating meat at the Pesach Seder?". Are those interesting to someone searching for 'meat'? Arguably not; in which case, perhaps we should not have a meat tag and instead have a slaughter-shochet-shecht and a milk-and-meat tag.
food and meat. Y'know, questions about "jewish food" (bagels and lox in US, etc)...
food or meat. (But see area51.stackexchange.com/proposals/23276.)
While I don't think we should get into the whole "hierarchical tags" type of thing, I do think coarse-grained + fine-grained are both useful.
Taking a different example, halacha, hilchot-shabbat, and shabbat.
Sure, we could just tag it with halacha and shabbat... but that's not really the same thing, and hilchot shabbat is a big enough subject of itself to merit its own tag. It also makes sense to encourage that level of specification...
No, it's not the same thing as shabbat, since there are plenty of questions and topics to discuss about Shabbat that are not hilchati in nature.
Also, if we were to just use the specific tag, and use only hilchot-shabbat, this removes those questions from the larger set of Shabbat and Halacha. This makes a difference, e.g. if you have a posek (or anybody with a halachic interest in the site) that is interested in all types of halacha questions to the exclusion of e.g. aggada or lamdanut questions. In the same manner, historians may be interested only in history, or high-school Tanach teachers (or Machon Herzog ;) ) interested in all tanach-scripture-bible questions. On the other side, you might have someone interested in learning anything they can about Shabbat - halachically, historically, experientially...
Hence, I would see all 3 tags (halacha, hilchot-shabbat, shabbat) as fitting, since you might be approaching that area (category+topic) from either direction.
food tag as coincidentally congruent with kashrut, sure they both involve food, but kashrut isnt really about the food... albeit many of the food questions should have been kashrut, but food really covers other non-kashrut areas.