This is a pretty neat trick to get your friend some extra marks if he or she is on the opposite faction. Ill do my best to explain it
This is how one scenario could be set up as. You are an alliance priest. Your friend is a horde and horde controls WG. Alliance is doing really well and is to the last gate. When the gate goes down, quickly MC your friend. When you MC him, he will technically be on the alliance and therefore will receive 3 marks instead of one.
This is similar to the old Halaa trick that got the opposing faction some battle tokens from your side's kills.
I know not many people will find this useful but it can help some people out