Excerpt from my latest Sasstrology post (please leave comments on the Sasstrology site).
"Synastry and composite aspects work in very different ways. The differences can be confusing, especially if the same planets are used. If the energies of the synastry and composite planets are the same, doesn’t that mean the impact on a relationship will be the same? Not at all. Understanding this is the key to handling the energies between you and your partner."