From the documentation and from the fact that pretty much every git user who's responded has told me the same things. Or am I supposed to take that as a massive coincidence?
http://pragprog.com/titles/tsgit/pragmatic-version-control-u...
The only person who suggested anything else, out of fifty-seven comments so far, was one who suggested merging the branch and then keeping it around rather than deleting and tagging it.
Since that's all I have to go on, and since it seems to be a pretty clear consensus, I'm taking their advice as being a generally-accepted convention amongst git users. Granted, such conventions in git seem to be as ephemeral as branches (e.g., fads such as "rebase everything! rebase after every commit! No, wait, never rebase! Rebasing is evil! Nobody should rebase!"), but if you're trying to suggest that as a result there are no conventions, I'm just going to write you off.