Thank you for your response. Would I be slowing down my components by using multiple?
With those power supplies Multiple rail mode just means that there is OCP (Over Current Protection) for each of the cables from the power supply. It's set to 40A, which is 480W at 12V, which is pretty unlikely to draw from a single cable under normal conditions. It's like a breaker for your PSU, like in your house if you have too much stuff plugged in to one outlet like a microwave and a toaster running at the same time or an electric heater and a TV plugged in to the same outlet. Setting to single rail mode just disables that 40A limit and lets it deliver as much power as the PSU can over any cable.
I would leave it in multi rail mode and if you have issues with the PC shutting down under load, switch it to single rail mode. Unless you're doing extreme overclocking like LN2 CPU cooling hitting 6GHz it's very unlikely you would ever draw enough power to trip the 40A limit.