Getting Started with LTspice
Noise analysis let you view the noise inherent in your system as well as injected noise from outside source when modeled properly. Noise is most commonly concerning in op-amp circuit where precision is everything. For example, a battery management system using op-amps to sense the current. Charging cycles of rechargeable batteries as well the load current are very important parameters to monitor for the overall health of the battery and safety of the user. A noisy op-amp circuit may skew that current reading and cause unwanted effects such as incorrect current readings on the microcontroller which keeps the battery from being over or under current. I'm sure an audio example would have been better to use here. But you get the idea, noise can be bad when it is unwanted.
We are going to continue using the pre-amplifer circuit from the Electret Mic Breakout Board and run a noise analysis. LTspice can model the [shot, flicker and thermal](https://en.wikipedia.org/wiki/Noise_(electronics) noise your circuit.