Only difference between modular - semimodular - nomodular psus is:
Modular - all the cables can be removed from the PSU.
Semi-modular - only the ATX and CPU cables cannot be removed, everything else can (sata, pci-e, etc)
Non-modular - all the cables available are on the PSU and you cant remove them.
So only difference is better cable management, nothing else. Just high-end PSUs are always modular.