I'm not going to get too much into detail as NPrinting and me don't get along. But one thing you have to keep in mind is licensing. Whereas Qlik Sense tokens are relatively expensive, you can has up to 250 report receivers from a standard NPrinting install. That greatly expands the amount of people who can benefit from your QS install, without incurring the the cost of each of them having a token.
Of course, this information is probably all wrong, but whatever.
You really can't produce formatted reports from Qlik Sense. You can export data to excel. Or whatever is currently on the screen to pdf or image. But that is about it.
If you want a nicely formatted report that is scheduled to run and distributed to users then you have to use nPrinting.
User can create their own sheets with visualizations in QS. But not reports.
I have a few clients that have decided to utilize N-printing along side of QS. The benefit is that many people don't want to make/have time to go in and do data discovery within the tool. N-Printing allows you to schedule pixel perfect reports to be mailed at any given time or when a given threshold is hit, just like with QV.
The licensing for N-Printing might be advantageous if you are trying to send out reports to a larger group of people.
As the guys have said nprinting expands on your investment in qlik without incurring costs for expensive user tokens. You can distribute to users that dont have a licence to use Sense.
Alot of your user community probably don't want to login and explore their data. what they want are snapshots of it at regular points in time. this is where nprinting comes in to schedule that distribution in a format that can be easily consumed offline (excel,powerpoint, pdf) and delivered to the user in a variety of ways. (email, newsstand, hub, folder)
It is a bit fiddly to get the hang of and some of the early versions of 17 were disappointing but 17.3 onwards they have started to get their act together.