Dynamic Subdivision and Saved Projects/Tools
Any Dynamic Subdivision settings applied to the current Tool or SubTool will be saved within either Project (ZPR) or Tool (ZTL) files. After saving and reopening a file, the current Dynamic Subdivision settings will remain the same.
Unlike Classic Subdivision which actually changes the model’s geometry, Dynamic Subdivision is a render effect being performed in real-time. As such, Dynamic Subdivision has no effect upon file size. ZBrush is simply storing a few settings rather than extra polygons.