JR Matchbox
 

The JR Matchbox is really neat BUT I sure wish they had made
it where instead of having input for 4 servos into 1 channel
it was divided up into two groups: Where you have input for
2 servos into one channel and 2 more into another channel.
Example: 2 ail servos in one side and 2 flap servos on the other
with 2 outputs to the receiver.
That way if someone wanted to use 4 servos together they could
simply Y the two outputs together.
I can't think of any application that would use 4 servos into 1
except maybe the TOC airplanes which gang servos together.

JR Matchbox
 

The leading edge slats on the BVM F-100 is one example.