Re: Two points
Or, for example, a national crisis may hit that requires the government to very suddenly and very quickly pay an unfathomable amount of money to almost every employer in the land to stop the economy collapsing under the weight of said crisis as everyone stays home.
Which is of course not a hypothetical. This was achieved by rapidly adapting existing sources of data and existing monetary flows from systems like HMRC's RTI (the thing that actually does your PAYE), and essentially reversing the flood of money back out to employers in record time.
"Simplify the system" is the refrain of simple people who don't really know what they're talking about.