What's the advantage of multiple 12v rails?

Is there any advantage in a power supply having multiple 12v rails? I've always heard that a single 12v rail is superior. Is that because of compatability with parts? You don't have to worry about which part is being powered by which rail, so you don't end up with two graphics both drawing power from a single rail that can't provide enough watts/amps?

I'm just not super educated on PSUs aside from which brands are generally decent to get.

The advantage of multiple 12v rails are mainly safety related. Less amps per rail = less boom should something actually go boom. Also less likelihood of taking other components. Outside of load balancing, not much difference between the two. However, a strong single rail can be indicative of better build quality. Cheap power supplies often use multi-rail designs, which kinda gives them a bad rep. I have a quad-rail 750w PSU that's been powering my  system for years, no issues.