You do not have to fill it out. It is an optional parameter of the Building object. I thought it was used in the model_create_prm_baseline_building method from openstudio-standards to create a 90.1 PRM baseline, but it is not (it instead uses some model_num_stories_spannedmethod and never sets the standardsNumberOfStories parameter.) parameter. So I guess it can be some metadata if you want to create measures that read those parameters.

TLDR;

Do not worry about it. It adds additional information to your model, but it is not directly translated into your EnergyPlus simulation.

You do not have to fill it out. It is an optional parameter of the Building object. I thought it was used in the model_create_prm_baseline_building method from openstudio-standards to create a 90.1 PRM baseline, but it is not (it instead uses some model_num_stories_spannedmethod and never sets the standardsNumberOfStories parameter. So I guess it can be some type of metadata if in case you want to create measures that read those parameters.

TLDR;

Do not worry about it. It adds is additional information that you can add to your model, model but it is not directly translated into your EnergyPlus simulation.