Well not to put too fine a point on it, but IMHO the most important mixes have not been mentioned....

While flight control mixing is useful for various conditions and is most commonly thought of as the actions mentioned already, I think you might find that being able to do a mix for throttle cut on shutdown, as well as a throttle up mix for flying are quite useful mixes as well.

Granted the DX-7 does have a throttle recovery feature that can be used to shut down a glow model, but I'm not really fond of that particular method as I'm used to using a tx switch with my gassers for shutdown. There are those guys who do like I used to, click in some throttle up trim just before takeoff and then you have to remember to click it back to land, or at least my Funtana doesn't want to land if the idle RPM is too high. So after being shown the switch activated throttle up trick, or what I call "Flight Idle" like a full scale turbine by the gasser guys, I find both mixes to work quite well.

As for flight control mixing to affect dynamic stability, there's nothing wrong with asking about it now, but the why will become clear as you get more experience...[8D]

You'll find that some mixes like the dual elevator servos must use one of the six mixes available. Be aware that if you are mixing flight controls, only #5 and #6 mixes on the DX-7 have the capability of trim following.