Show in "View Data"

I believe that once I uncheck "show in view data" option on item properties tab, then the respective item shall not be implemented into NSF as there is no data to store. In other words, such items exist only in application.xml and during runtime.

However, with Domino Leap 1.1 I can see that all my items are mapped into NSF, regardless "show in view data" is checked or not. Therefore a lot of unnecessary items gets stored into NSF (auxiliary items used for service calls, for computation of rules, etc.)

Is it an expected behavior? Or is my assumption wrong?

This is expected. The show in view data just stops the item from appearing in View Data, but we still capture and store the data.

Interesting. What is the reason to clutter backend NSF files with dozens of useless auxiliary items? I thought that such items needed to exist only at runtime...

You are placing more meaning into the function of that checkbox property. It is not intended to make the item "transient" (meaning not stored). We do need a setting like that, but it has not been implemented as of now.