Benefit Conferred theory measures the value of the enrichment or benefit conferred on someone else.
Past act leads to a subsequent promise.
In Webb v. McGowen or Cotnam v. Wisdom if given the opportunity to bargain, both defendants most likely would have made the bargain. Implied material benefit was conferred to the promisor in Webb. If the wife had made the promise to pay maintenance, then we could look at reliance factor and promisory estoppel. So the main distinction between Mills v. Wyman and Webb v. McGowen is who made the promise. If it is a gift, then not enforceable.