What is this sentence pattern?
Although it is not necessary, this detail may come in handy later on.
Does this "it" mean "this detail"?
Like:
Although he is the first black president, Obama has not yet made much out of his blackness.
At first, you don't know who "he" is, but later you find out that it means Obama.
Is this construction common?
Solution 1:
A pronoun looking forward for its referent (the term which 'defines' it) is common and acceptable in all registers. The technical term is cataphora
However, cataphora is subject to one restriction: the referent cannot fall in a constituent subordinate to the constituent containing the pronoun, only in a coordinate or superordinate constituent. For instance:
okAlthough it is not necessary, this detail may come in handy later on. ... The pronoun, it, is in a subordinate clause and its referent, this detail, is in the main clause, so this is OK, even though the pronoun looks forward to its referent.
okIt may come in handy later on, but this detail is not necessary. ... The pronoun, it, looks forward to its referent, this detail, but this is OK because the referent lies in a coordinate clause.
∗ It may come in handy later on, although this detail is not necessary. ... The pronoun, it, looks forward to its referent, this detail, and this is not OK because the referent lies in a subordinate clause. A reader who encountered this sentence would look to the previous sentence for the referent.
Solution 2:
Both of the example sentences are examples of pronoun coreference. When we use a personal pronoun, we expect listeners to know who we're referring to, and there are grammar rules about that.
In particular, the rule for English pronouns says that a personal pronoun may follow its antecedent
- Bill likes chili although he is a vegetarian. (Bill = he)
And a pronoun may also precede its antecedent,
- Although he is a vegetarian, Bill likes chili. (Bill = he)
provided the pronoun does not command its antecedent
(which basically means that the pronoun must occur in a clause that is
subordinate to the clause in which its antecedent occurs).
I used to use this as an exam problem in my undergraduate Intro class.
The simplest answer is that a pronoun may not both precede and command its antecedent.