I posted this on anoher thread, but I think people missed it or didn't realise how nice this is:
It allows my brain to set the focus of my mage alts for cc from the brain window and then cast polymorph from the brain window without leaving my brains window
So for me it like having a Pally with 3 seamless CCs

I'm making use of the targettarget approach to macros that Zzyzxx71 suggested in this thread: Oooh new assist without focus macro!!

my follow macro for the alts (I only put the brain in as it was a quick test):

/target [target=Aztrid];
/follow

my focus macro on the mage window bound to numpad 1:
/focus [target=targettarget,exists] target

my sheep macro on the mage window bound to numpad 2:
/#showtooltip Polymorph
/cast [target=focus] Polymorph

so I select a target with my brain and hit numpad 1, the mob is now focussed for the mage

I select another mob for dps which is my targettarget

I hit 2 and the mage sheeps the focussed mob and I can then get it to DPS my selected target as it's using targettarget NOT focustarget.

I never once left the brains' window I've found this to be very quick when things go pear shaped, it's great not to have to click over to the mage screen and lose valuable seconds trying to select a mob from a slightly different pov for cc when all hell is breaking loose.

<edited for clarity>