Optimize Cameras only with check points increase accuracy

[Podmiot]

Hello! 
I have a problem with "Optimize Camera" and I can't figure out how it works in my case. Unfortunately, I could not find a similar case on that forum.

I have project with camera reference obtained with use of PPK method with accuracy about 10 cm and GCP measured by GPS with accuracy about 2 cm.

I carried out a test running in the following steps:
1. Align photos
2. Gradual selection -> Projection accuracy to level 10
3. Optimize Cameras
4. Import and indicate all markers on photos
5. Uncheck all of markers to use them as check points (direct georeferencing)
6. Without any other changes "Optimize Cameras" again

I have noticed that values of Error (m) and Reprojection error change. All markers was unchecked so I think that nothing should change becouse check points should not increase accuracy. Does this mean that check points are, however, taken into account in the optimization?

[JMR]

check-points (unchecked ground control points) will play some role in the optimization as they are tie points placed by user, thus it is normal that project adjustment statistics change a bit if you opimize after having added check points. If you do not trust your hability to pick a point well, simply do not re-optimize.
Regards

[Podmiot]

Thank you very much for your answer