Whatever floats your boat. LOL @ the add people together and divide by two. You're taking two people's natal and creating one brand new natal. I think of a composite as a chart of the relationship itself, as 2 people coming together and combining energies. Synastry shows the individuals as they relate to each other in their own environment, how they complement each other. I use them both with no accuracy dilemmas with either. I like using the transits with a composite chart, shows how the relationship develops over time, static shows up in transits for sure. Some astrologer friends of mine use progressions with the composite charts as well.

Robert Hand's textbook Planets in Composite is handy and may make it easier to comprehend.

http://www.cafeastrology.com/compositechart.html

CC