It integrated with "Function panels". Function panels were our attempt at documenting our library functions. See the second link below. But you could enter values, declare variables, etc and then run the function panel. Behind the scenes, the code is inserted to the interactive window and then run. Results are added back to the function panel.
These also worked while suspended on a breakpoint in your project so available while debugging.
My understanding was that these features were quite popular with customers. They also came it handy internally when we wrote examples and did manual testing.
https://www.ni.com/docs/de-DE/bundle/labwindows-cvi/page/cvi...
https://www.ni.com/docs/de-DE/bundle/labwindows-cvi/page/cvi...
https://irkr.fei.tuke.sk/PPpET/_materialy/CVI/Quick_manual.p...