One benefit of distributed checks is that they are more predictable: doesn't matter how busy or not the rest of the airport is, your queue length doesn't change. TXL had that setup (independent security for a pair of gates each) for the older areas and leaving from those terminals was really fast and reliable. Sure, duty-free was tiny then (since also only for a pair of gates), but that never really mattered to me.

I guess for a hub like Singapore it might also make it easier to adjust checks done for different destinations?