It’s a money spinner for central government, obviously. I’m not saying it’s some kind of conspiracy, but someone somewhere is obviously making a decent amount of money, intentionally or not.
In terms of the locals, that always makes me laugh because whenever these schemes are introduced, the first people to get caught are usually the ones complaining about speeding in the first place. Such people are normally the types that drive at 35 everywhere and then complain about “lunatics” overtaking them at 50-60 in an NSL.
If you’ve ever actually tried to drive at 20 for an extended period of time, you’ll notice that it’s very, very slow. Most normal drivers slow to 20 when there’s an obvious hazard, then continue at 30, but a lot of councils seem to want to install blanket 20 limits to appease professional complainers.