As it costs ISP's it is clearly a place where throttling can save real cash.
Actually, I think that's a fallacy. It is true in markets where accounts are unmetered, but NZ has metered accounts. ISPs charge per byte, and make a profit on every byte they deliver. Therefore, there should be no incentive to not deliver a byte.
The only issue would be if a prime time byte was more expensive than an off-peak byte (which it probably is). If that's the case, they should offer a discount on off-peak to shift discretionary traffic to overnight. Much better way to deal with it. As it stands, I have no incentive to delay any bulk transfers, so I don't.
As long as the incremental cost per byte is covered by the charge, there is no reason for the ISP to not act as the best bit pipe they can.
Which is why ISPs like SNAP are doing so well.
so do power companies, and since being privatised there is less and less incentive to have spare capacity, so when there's a problem/outage it means that a lot of people face power cuts due to not having enough power.
basically if you spend money on capacity you don't need, and you just charge per gb, then you're wasting money paying for bandwidth you're not using, so it encourages financially-motivated businesses to keep tight margins on bandwidth.
if you look at https://www.ams-ix.net/technical/statistics for instance, it's common for bandwidth usage to vary depending on time of day. that's a peering exchange with nice easy graphs to view, and i expect nz to have slightly higher overnight usage as a significant number of users have either slow connections or off-peak advantages. but one thing to note in that is even on a huge peering exchange doing heaps of traffic there is a significant bias towards the evening having higher traffic but if more capacity is bought it'll only cover the peak time traffic, so there's less return on investment.
which is a little similar to what's happening with power. the first line of defense with power is to start turning how water off, and give people a reduced power rate if they allow this. the second is high volume users that can vary their loads are charged rolling rates based upon demand. (so if power station fails they can just switch off and lose some production or such, and in return get cheaper rates most of the time), and the third is rolling blackouts where power is cut on purpose to keep up with demand.