Some people schedule downloads to start and stop at certain times, so they don't have to be awake.
It's more relevant to Anytime / Night packages, for example :
EDIT - link should work now :
anyone else struggling recently? I'm getting
mybroadband.co.za
I usually see to my downloads manually when I wake up during Night data times.
But I think what your question revolves around in the 1st place, is why is it offered ?
Primarily for those who are cost sensitive, like myself, and prepared or forced to make concessions by making do with peak hours being taken away, for which they charge considerably more on these uncapped deals.
Also, can be a backup for those on fibre that covers a majority of the day, at a very reasonable cost in their view.
Any number of reasons ; I've often considered switching to it, but for now am getting all that's needed from capped LTE.