What is the point of fully modular?

why not just get semi-modular you are always going to need those connecters so whats the point of having them detachable

I like to leave the cables tied in place, remove the heavy power unit, whenever I transport my case.

Easier to sleeve the individual cables.

Can replace any and all damaged cables.

Also, it's a cleaner aesthetic, in my opinion.

Could also replace the power unit without touching the cables.

Maybe you could also use two power supplies if you have an insanely power-hungry setup, of which only one would need the motherboard connections? Is that a thing?

Also, messed up cable does not ALWAYS mean new power supply. 

Yes, you can use two PSUs in one system.