If you are performing a longitudinal study with your research, you would have multiple observations/interviews of your participants performed at a certain time.
This will bring you multiple files for a specific participant.
In such a situation, you would need to follow a slightly different case creation process in Nvivo.
In this video I tried to show to how you can assign multiple files to a case so that you can create case attributes and perform queries for each participant's attribute values.
I hope this will be helpful.