There just "excess bagage" on those set ups. Remember; you now have 2 idle ports with the same vacuum. They tend to stall (to rich) cold anyway W/O any choke.
If you had one with 3 carbs, then the center one is sometimes used (with choke) as the end idle mixture screws are turned in 'all the way' (off) and the engines idles only on the center carb and often has "progressive" linkage as Larry points out.
It works best (all around) this way and looks a lot clearner. You just need to warm up before driving, which is best anyway.
