Analog I/O's

When considering analog I/O's, for what applications shud one consider differential I/O's, and what is the basic difference between the single ended analog input modules and differential input modules w.r.t application. Where can we consider single ended input modules.

1.
Signal noise and noise propagation.

With single ended I/O if you have noise on one channel the noise will affect all signals on the card through the common.

2. With single ended I/O modules you cannot mix power sources, with differential you can. So.... If you have a mixture of 2-wire and 4-wire devices, you cannot use single ended.