Low Dropout regulators are typically used where there is no "headroom to play with''. Anyone here remember that term??
For example: A raw, smoothed PSU that barely puts out the the required Voltage....never mind the stuff coming in...And it must still regulate the Output despite the Input Voltage..
Solar Panels are favourites. Why did I say that?
Essentially, they regulate the Output Voltage with minimal Power loss across the Series Transistor. Hence the term " low dropout"....
Minimal power loss with Regulation as well......someone is going to shoot me down here.
Bring it on. Sigh.
Never mind. I shot myself in the foot anyway.
Anyway. LM317T is around 2.5V. Low Dropout regulators are about quarter of that.