Usually, where one or more parties happen to be on signing a contract should have no bearing on that contract. It might be relevant for purposes of determining the governing law, but only if you fail to include a governing-law provision.
So a general matter, nothing is accomplished by stating—whether in the introductory clause, in the signature blocks, or elsewhere—where one or more signatories happen to be when they sign the contract.
But at a recent seminar in Europe, one of the participants said that under the law of a country that has now slipped my mind (Portugal? Italy?), where the parties enter into a contract can have tax implications.
I’d like to know more about that or any other circumstances where it makes sense to state where the contract is being entered into.