Single Rail vs. Multi-Rail Power Supplies

I honestly am not able to understand the benefits that would be realized by implementing a multi-rail power supply over that of a single rail design of identical power output levels.



I can possibly see some downsides such as possibly parts count and circuit design complexity going up which, to me, would lead to less reliability. My thoughts also extend to those power supply designs that can, via firmware, be reconfigured to operate in a single rail mode. Also, if the individual rails couldn't be reconfigured into a single rail, you could run the risk of overloading one of the rails.



Please help me understand what the benefits of a multi-rail system are.



Thanks in advance!