Practical design implications of noise analysis

[centaurus01]

Literature has many examples of how to calculate the input referred noise in a circuit. It is usually done by specifying current and voltage noise squared at the input and considering the circuit noiseless.
When we actually design circuits, how is this analysis useful? Are there any other implications apart from knowing the noise floor at the input?

From what I get so far, the noise analysis seems to be very practical to design the resolution of ADC or DAC. But, how is it actually useful in, say, sizing the transistors?

 

[crutschow]

Noise analysis is useful to determine if your circuit will meet the noise requirements for its intended purpose. If it doesn't then you need to modify the design so that it does. Among the factors affection noise are the size of transistors, their operating current and the value of resistors at sensitive nodes.