The most important metric for "too localized" is "how many people could this ever help?". If the answer is "only the one person who asked the question", it's too localized.
There are some indicators to help determine this:
- relevant only to a very small number of people (e.g. users of a particularsingle SharePoint installation)
- specific to a point in time (e.g. "When will SharePoint v.Next be released?")
- impossible or extremely difficult to reproduce the situation described
It's important to close these questions for the same reasons that we want to remove or discourage anything else regarded as "noise" in the site - we want a site of high quality that attracts and engages people. Sifting through questions that can't be answered isn't interesting or fun.