While the experience of individuals will be mostly limited to one particular field and likely a specific geographic area (e.g. Europe or U.S.A. or Australia etc.), I believe we should strive for answers that generalize across all fields and areas. Otherwise the utility of any particular question and answer is severely limited in scope.
In anecdote, so far on the site I haven't seen any general advice given by individuals in STEM fields that don't in large part apply to social sciences. In general (I suspect) were likely to find more similarities than differences.
Hopefully as the site grows differing perspectives become represented, so if pertinent differences between fields exist for any particular question they are noted, but I don't think assuming a priori that differences exist is a good idea. And forcing tags naturally perpetuates such an artificial division.
To reify my perspective in address to the comments by @eykanal and @Henry, I think it best to be more specific about what I mean when I say advice should generalize to all fields. This does not simulataneously mean the answer is broad (and purportedly unuseable)!
The vast majority of posters on the site so far are not from social science fields, yet it is difficult to come up with answers that, at least in some respects (if not entirely) are applicable to my personal experiences (criminology graduate student in the USA).
For examples of questions/answers by people not within my field, but the responses IMO would be reasonable to generalize to my field;
You could arbitrarily insert into any of these questions specific field X (e.g. "How important are my grades to the rest of my PhD career in Mathematics"), but this immediately implies that experiences in other fields are not pertinent (which is not the case). Nor are the answers to the above "too broad to be useful" because they generalize across multiple fields.
It is difficult to say much more speaking widespread about the site (so far we have all made very general statements, and we could all find anecdotal situations as evidence for our positions). But I don't see how suggesting such a tag system is benifitial to the site, and I believe it could be harmful.
Asking for clarification on questions seems to be a regular occurence across the SE sites. Although it can be annoying at times, it is not a noxious enough problem to need such a novel solution as you are presenting.
As a side note, although I understand the motivation of the original poster, the proposed usage of tags in this instance is a "meta" tag. See the SO blog post by Jeff Atwood on the subject, The Death of Meta Tags for why such tags should be avoided. Although you could probably argue for their utility in other respects, they certainly don't describe the content of the question.