I have been wondering about the same. I have not been able to find one good article which could explain this matter. I can only see that it's not something to discuss. But I would like to know why too.
NPrinting consumes an extra license when you run it on an additional service account.
Perhaps segregation of services can be relevant, but I don't see the smoking gun. What have I missed?
Qlik support might only be able to give you the official answer...
We have set up NP16 in a QV11 server and we are using the same service account in NP. Nothing is wrong.
The only thing is that we set up the reload tasks in QV management console very early in the morning and NP schedules later than that to avoid the same service account running for both QV and NP at the same time.
We recently are investigating using Qliksense + Nprinting, and get the same suggestion from our QV service agency. So I would like to know why. Because our current solution Nprinting 16.3 and QV 11.20 SR15 are in the same server and works perfectly for a long time.
As I see you are using Nprinting 16.4, which I know do has some issues, even more issues than 16.3, I suggest you to update to Nprinitng 16.5, you can check the fixed issues for 16.4 in the release notes.