Applications of LDO's are broad ,some examples.:
- Multiple output SMPS's (e.g flyback).Used to provide tight regulation of additional windings. The windings that are only loosely regulated by the transformer turns ratio. These winding aren't immune from line variations so an LDO depending on power requirements can be used.
- The main advantage is they can provide regulation with a very small input output differential.Since the main losses of linear regs are in the pass element this means they can be very efficient ( P = EI). In some applications e.g. ( BATTERY low power) small handheld portable RF devices reduced complexity and the lack of RFI,EMI makes them a better choice then an SMPS. There is some noise primarily the reference and pass element but minuscule compared to an SMPS with its fast transitioning waveforms.