Why does enabling engine sync on the MD-80 series trigger the "Master Caution" light?
AFAIK The reason you aren't supposed to take off/land with prop or engine sync on is because if the leader engine fails, the follower engine will reduce power to match it, and that is really not ideal, especially low and slow, a la V1 cut or failure on short final. Try it out- fail the leader engine just after V1 and see what happens!