The gemara (B.M. 47a) presents a machlokes between Rav and Levi whether a kinyan chalipin is done b’keilav shel koneh or keilav shel makneh, using the token of the buyer or seller. The gemara explains the reasoning of Levi that the kinyan is done using keilav shel makneh: the hana’ah (benefit) gained by having his symbolic token gift accepted by the koneh is sufficient consideration for the makneh to consent to the larger deal.
Last post I mentioned the gemara (Kiddushin 7) that even though marriage is normally effected by the groom giving something of value to the bride, where the groom is a very distinguished person (e.g. an aristocrat), the kiddushin can be effected by his accepting a gift from the bride – the hana’ah (benefit) gained by the bride having her token gift accepted is itself of sufficient consideration for the marriage to occur.
The Rishonim (Ramban, Rashba, Ran) point out a discrepancy between these cases – the case of kinyan chalipin applies to any two parties making a deal; the case of kiddushin applies only to a woman whose gift is accepted by a distinguished person, adam chashuv. Why the discrepancy? (Or, to approach the question slightly differently, why does Rav disagree in the former case, but not the latter?)
While you are mulling that over, R’ Chaim Scheinberg quotes a Pischei Tshuvah which suggests that if you give mishloach manos to an adam chashuv, the hana’ah you receive by having your food gift accepted by this adam chashuv allows him to fulfill his mitzvah of mishloach manos by accepting your gift! Yet, no other achronim suggest such an idea – why not?