we use the mizzen for many things.
first it allows a sail plan with a lot of canvas and shorter masts.
i believe this is better for offshore work.
secondly, we regularly sail with Jib and jigger in 50 + knots and a very nicely balanced helm.
thirdly we can run a spinnaker and a mizzen spinnaker.
this trip south we hit a new surfing speed of 16.7 knots (yes i have a photo of the knotmeter)
as you said it is also a great place for a radar antenna. but for me the heavy weather aspects are great.