I know there's been much discussion about the value of mizzens on here already.
Will be interested to learn what the performance perspective may be?
Personally, on a BRe, my mizzen is most effectively Used to stay head to wind when getting the main up, or when at anchor.
Seems to be needed to counter the weathercock effect of the small cabin, otherwise my boat seems to prefer to lie stern to wind.
Also use the mizzen as something of a roll damper when motoring, especially when fishing.